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    <link:label id="lab_us-gaap_OperatingLeaseLiability_fce130c8-f473-47aa-addd-433b39e3b76a_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeaseLiability" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Lease, Liability</link:label>
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    <link:label id="lab_us-gaap_PlanNameDomain_74dc7fe7-3a7b-4cad-b967-6ec738aed254_terseLabel_en-US" xlink:label="lab_us-gaap_PlanNameDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Plan Name [Domain]</link:label>
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    <link:label id="lab_us-gaap_AccountsReceivableNetCurrent_7e681167-c13c-4275-89ad-3d6ab1cb6195_terseLabel_en-US" xlink:label="lab_us-gaap_AccountsReceivableNetCurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accounts receivable, net of allowance of $643 and $585 as of June 30, 2020 and December 31, 2019, respectively</link:label>
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    <link:label id="lab_us-gaap_NonoperatingIncomeExpense_9beb3398-e080-4cea-9997-5365fdeb3797_totalLabel_en-US" xlink:label="lab_us-gaap_NonoperatingIncomeExpense" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total other income, net</link:label>
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    <link:label id="lab_us-gaap_AdditionalPaidInCapital_20bbd9c8-61a3-4575-a4b8-eca5e4b9a152_terseLabel_en-US" xlink:label="lab_us-gaap_AdditionalPaidInCapital" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Additional paid-in capital</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock_24d23fa6-66c4-4da1-98df-fe188477934c_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Employee stock-based compensation</link:label>
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    <link:label id="lab_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_7cd5bbc8-4b8f-400a-b1ff-44a22b0cb92e_terseLabel_en-US" xlink:label="lab_us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Prepaid expenses and other current assets</link:label>
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    <link:label id="lab_us-gaap_IncomeTaxDisclosureAbstract_5025e167-392c-45f8-85cb-7e46d00179ef_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeTaxDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Tax Disclosure [Abstract]</link:label>
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    <link:label id="lab_us-gaap_CertificatesOfDepositMember_d8a0becc-d125-4715-aa30-a6aab57dc447_terseLabel_en-US" xlink:label="lab_us-gaap_CertificatesOfDepositMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Certificates of Deposit [Member]</link:label>
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    <link:label id="lab_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_931cac9e-7a6b-4687-83c2-9f171ede805e_terseLabel_en-US" xlink:label="lab_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Foreign currency contract, asset, fair value disclosure</link:label>
    <link:label id="lab_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_label_en-US" xlink:label="lab_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Foreign Currency Contract, Asset, Fair Value Disclosure</link:label>
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    <link:label id="lab_qlys_ForeignCurrencyContractPoundMember_documentation_en-US" xlink:label="lab_qlys_ForeignCurrencyContractPoundMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Foreign Currency Contract, Pound [Member]</link:label>
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    <link:label id="lab_us-gaap_CashAndCashEquivalentsMember_5c4ad5e3-0167-43c1-8617-aecd72c477c6_terseLabel_en-US" xlink:label="lab_us-gaap_CashAndCashEquivalentsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash and cash equivalents:</link:label>
    <link:label id="lab_us-gaap_CashAndCashEquivalentsMember_label_en-US" xlink:label="lab_us-gaap_CashAndCashEquivalentsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash and Cash Equivalents [Member]</link:label>
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    <link:label id="lab_us-gaap_OperatingLeaseLiabilityNoncurrent_328f86a0-f18f-44e6-a3e0-542cee8a0ee6_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Lease, Liabilities, Noncurrent</link:label>
    <link:label id="lab_us-gaap_OperatingLeaseLiabilityNoncurrent_label_en-US" xlink:label="lab_us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Lease, Liability, Noncurrent</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
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    <link:label id="lab_us-gaap_OperatingExpensesAbstract_eb9fea8e-8ad0-429d-9217-e3aaa4910eab_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingExpensesAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating expenses:</link:label>
    <link:label id="lab_us-gaap_OperatingExpensesAbstract_label_en-US" xlink:label="lab_us-gaap_OperatingExpensesAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Expenses [Abstract]</link:label>
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    <link:label id="lab_us-gaap_RepurchaseAgreementsMaturities_label_en-US" xlink:label="lab_us-gaap_RepurchaseAgreementsMaturities" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Repurchase Agreements, Maturities</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepurchaseAgreementsMaturities" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RepurchaseAgreementsMaturities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RepurchaseAgreementsMaturities" xlink:to="lab_us-gaap_RepurchaseAgreementsMaturities" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PreferredStockSharesAuthorized_dbb65609-0071-4a6f-a893-d3330b214559_terseLabel_en-US" xlink:label="lab_us-gaap_PreferredStockSharesAuthorized" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Preferred stock, shares authorized</link:label>
    <link:label id="lab_us-gaap_PreferredStockSharesAuthorized_label_en-US" xlink:label="lab_us-gaap_PreferredStockSharesAuthorized" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Preferred Stock, Shares Authorized</link:label>
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    <link:label id="lab_us-gaap_StockholdersEquityAbstract_bceb4ac7-2513-4cdc-8da9-8ab950e395c5_terseLabel_en-US" xlink:label="lab_us-gaap_StockholdersEquityAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Stockholders&#8217; equity:</link:label>
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    <link:label id="lab_qlys_ScannerAppliancesMember_68eb582c-e698-486c-a793-96d7f5159288_terseLabel_en-US" xlink:label="lab_qlys_ScannerAppliancesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Scanner appliances</link:label>
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    <link:label id="lab_us-gaap_OperatingLeasePayments_17a02672-f851-426a-bce5-e0d15f88c5f1_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeasePayments" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Lease, Payments</link:label>
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    <link:label id="lab_us-gaap_RetainedEarningsMember_label_en-US" xlink:label="lab_us-gaap_RetainedEarningsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retained Earnings [Member]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RetainedEarningsMember" xlink:to="lab_us-gaap_RetainedEarningsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_qlys_ScannerAppliancesAndOtherComputerEquipmentSubjectToSubscriptionMember_e9e3272b-f71a-48c1-8414-f5f96ad0dca9_terseLabel_en-US" xlink:label="lab_qlys_ScannerAppliancesAndOtherComputerEquipmentSubjectToSubscriptionMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Scanner appliances and other computer equipment subject to subscription</link:label>
    <link:label id="lab_qlys_ScannerAppliancesAndOtherComputerEquipmentSubjectToSubscriptionMember_label_en-US" xlink:label="lab_qlys_ScannerAppliancesAndOtherComputerEquipmentSubjectToSubscriptionMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Scanner appliances and other computer equipment subject to subscription [Member]</link:label>
    <link:label id="lab_qlys_ScannerAppliancesAndOtherComputerEquipmentSubjectToSubscriptionMember_documentation_en-US" xlink:label="lab_qlys_ScannerAppliancesAndOtherComputerEquipmentSubjectToSubscriptionMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Scanner appliances and other computer equipment subject to subscription [Member]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_qlys_ScannerAppliancesAndOtherComputerEquipmentSubjectToSubscriptionMember" xlink:to="lab_qlys_ScannerAppliancesAndOtherComputerEquipmentSubjectToSubscriptionMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LesseeOperatingLeasesTextBlock_92bc9be7-7f1f-4470-807d-a3403cc7197a_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeasesTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Leases</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeasesTextBlock_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeasesTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Leases [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeasesTextBlock" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeasesTextBlock"/>
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    <link:label id="lab_qlys_ShareBasedCompensationPercentageOfSharesThatWillVestUponTrigger_documentation_en-US" xlink:label="lab_qlys_ShareBasedCompensationPercentageOfSharesThatWillVestUponTrigger" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-Based Compensation, Percentage Of Shares That Will Vest Upon Trigger</link:label>
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    <link:label id="lab_qlys_OtherIncomeExpenseNetAbstract_2ce210c5-3d83-4312-ad7b-2a8ad3c8e504_terseLabel_en-US" xlink:label="lab_qlys_OtherIncomeExpenseNetAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other income (expense), net:</link:label>
    <link:label id="lab_qlys_OtherIncomeExpenseNetAbstract_label_en-US" xlink:label="lab_qlys_OtherIncomeExpenseNetAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Income (Expense), Net [Abstract]</link:label>
    <link:label id="lab_qlys_OtherIncomeExpenseNetAbstract_documentation_en-US" xlink:label="lab_qlys_OtherIncomeExpenseNetAbstract" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Income (Expense), Net [Abstract]</link:label>
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    <link:label id="lab_dei_DocumentPeriodEndDate_c69cfe6b-a378-4048-a700-a06a99001237_terseLabel_en-US" xlink:label="lab_dei_DocumentPeriodEndDate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Document Period End Date</link:label>
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    <link:label id="lab_us-gaap_FinanceLeaseLiabilityPaymentsDueYearFive_70bb141c-c111-4537-a577-92ce018a2529_terseLabel_en-US" xlink:label="lab_us-gaap_FinanceLeaseLiabilityPaymentsDueYearFive" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Finance Lease, Liability, Payments, Due Year Five</link:label>
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    <link:label id="lab_us-gaap_StatementTable_b80b9af2-d6cb-493f-9224-0511909b66b4_terseLabel_en-US" xlink:label="lab_us-gaap_StatementTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statement [Table]</link:label>
    <link:label id="lab_us-gaap_StatementTable_label_en-US" xlink:label="lab_us-gaap_StatementTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statement [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StatementTable" xlink:to="lab_us-gaap_StatementTable" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_EntityRegistrantName_014a7917-183b-43a6-bb25-25335eb64f95_terseLabel_en-US" xlink:label="lab_dei_EntityRegistrantName" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Registrant Name</link:label>
    <link:label id="lab_dei_EntityRegistrantName_label_en-US" xlink:label="lab_dei_EntityRegistrantName" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Registrant Name</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityRegistrantName" xlink:to="lab_dei_EntityRegistrantName" xlink:type="arc" order="1"/>
    <link:label id="lab_qlys_AntidilutiveSecuritiesAbstract_b0353a9c-30f3-4835-a4b6-9f8c21f856e7_terseLabel_en-US" xlink:label="lab_qlys_AntidilutiveSecuritiesAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Antidilutive Securities</link:label>
    <link:label id="lab_qlys_AntidilutiveSecuritiesAbstract_label_en-US" xlink:label="lab_qlys_AntidilutiveSecuritiesAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Antidilutive Securities [Abstract]</link:label>
    <link:label id="lab_qlys_AntidilutiveSecuritiesAbstract_documentation_en-US" xlink:label="lab_qlys_AntidilutiveSecuritiesAbstract" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Antidilutive Securities [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_qlys_AntidilutiveSecuritiesAbstract" xlink:href="qlys-20200630.xsd#qlys_AntidilutiveSecuritiesAbstract"/>
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    <link:label id="lab_qlys_BusinessCombinationDeferredConsiderationPaymentPeriod_500861d2-1410-4610-bf0c-edbe7bddfadc_terseLabel_en-US" xlink:label="lab_qlys_BusinessCombinationDeferredConsiderationPaymentPeriod" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Business Combination, Deferred Consideration Payment Period</link:label>
    <link:label id="lab_qlys_BusinessCombinationDeferredConsiderationPaymentPeriod_label_en-US" xlink:label="lab_qlys_BusinessCombinationDeferredConsiderationPaymentPeriod" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Business Combination, Deferred Consideration Payment Period</link:label>
    <link:label id="lab_qlys_BusinessCombinationDeferredConsiderationPaymentPeriod_documentation_en-US" xlink:label="lab_qlys_BusinessCombinationDeferredConsiderationPaymentPeriod" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Business Combination, Deferred Consideration Payment Period</link:label>
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    <link:label id="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_ca234250-7eb2-4543-b2ba-326040c347ba_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill and Intangible Assets, Net</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:to="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_qlys_AccumulatedDepreciationCapitalLeases_2692243d-c2cf-47a3-b174-6d73b70dd1e4_terseLabel_en-US" xlink:label="lab_qlys_AccumulatedDepreciationCapitalLeases" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Capital leases, accumulated depreciation</link:label>
    <link:label id="lab_qlys_AccumulatedDepreciationCapitalLeases_label_en-US" xlink:label="lab_qlys_AccumulatedDepreciationCapitalLeases" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated Depreciation, Capital Leases</link:label>
    <link:label id="lab_qlys_AccumulatedDepreciationCapitalLeases_documentation_en-US" xlink:label="lab_qlys_AccumulatedDepreciationCapitalLeases" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated Depreciation, Capital Leases</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_qlys_AccumulatedDepreciationCapitalLeases" xlink:href="qlys-20200630.xsd#qlys_AccumulatedDepreciationCapitalLeases"/>
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    <link:label id="lab_us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_14bc93d1-e8fd-44ee-a05c-823fadb1a9b4_negatedLabel_en-US" xlink:label="lab_us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Principal payments under finance lease obligations</link:label>
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_63f75486-d35a-4570-a063-9e76f8bce6f3_terseLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash flow from investing activities:</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:type="arc" order="1"/>
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    <link:label id="lab_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_5fe36f5c-1323-4d99-9fa2-01a05a8c2f40_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Purchases of property and equipment</link:label>
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    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_1277cd4e-51e6-4f90-bd56-0afc91b8f653_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Liability, Payments, Due Year Five</link:label>
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    <link:label id="lab_qlys_LeaseExpense_6d230edc-407c-4727-9765-066fea899900_terseLabel_en-US" xlink:label="lab_qlys_LeaseExpense" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lease, Expense</link:label>
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    <link:label id="lab_qlys_LeaseExpense_documentation_en-US" xlink:label="lab_qlys_LeaseExpense" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lease, Expense</link:label>
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    <link:label id="lab_qlys_NoncurrentAssetsMember_documentation_en-US" xlink:label="lab_qlys_NoncurrentAssetsMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Noncurrent Assets [Member]</link:label>
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    <link:label id="lab_us-gaap_ProvisionForDoubtfulAccounts_09356db6-2af7-408f-9f6a-0712a6799ad8_terseLabel_en-US" xlink:label="lab_us-gaap_ProvisionForDoubtfulAccounts" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accounts Receivable, Credit Loss Expense (Reversal)</link:label>
    <link:label id="lab_us-gaap_ProvisionForDoubtfulAccounts_label_en-US" xlink:label="lab_us-gaap_ProvisionForDoubtfulAccounts" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accounts Receivable, Credit Loss Expense (Reversal)</link:label>
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    <link:label id="lab_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_ab7b9dc1-57dc-40e7-9d41-870628edefc1_terseLabel_en-US" xlink:label="lab_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Unrecognized employee compensation cost, period for recognition</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax"/>
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    <link:label id="lab_us-gaap_AccountingPoliciesAbstract_6c6d0575-7f0d-4afd-ac90-d132f289ecb1_terseLabel_en-US" xlink:label="lab_us-gaap_AccountingPoliciesAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accounting Policies [Abstract]</link:label>
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    <link:label id="lab_us-gaap_AdditionalPaidInCapitalMember_00e1956e-9e2c-4fa9-a064-7283be2a1b74_terseLabel_en-US" xlink:label="lab_us-gaap_AdditionalPaidInCapitalMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Additional Paid-In Capital</link:label>
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    <link:label id="lab_us-gaap_RevenueFromContractWithCustomerTextBlock_05714df0-7b16-4b6b-8198-4b855f31f63f_terseLabel_en-US" xlink:label="lab_us-gaap_RevenueFromContractWithCustomerTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Revenue from Contracts with Customers</link:label>
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