Exhibit 99.1

Qualys Announces First Quarter 2021 Financial Results

Revenue Growth of 12% Year-Over-Year

GAAP EPS: $0.01; Non-GAAP EPS: $0.74

Raises 2021 Revenue Guidance to $402.5-$404.5 million

FOSTER CITY, Calif., – May 5, 2021 – Qualys, Inc. (NASDAQ: QLYS), a pioneer and leading provider of disruptive cloud-based IT, security and compliance solutions, today announced financial results for the first quarter ended March 31, 2021. For the quarter, the Company reported revenues of $96.8 million, net income under United States Generally Accepted Accounting Principles (“U.S. GAAP”) of $0.2 million, non-GAAP net income of $29.8 million, Adjusted EBITDA of $44.6 million, GAAP net income per diluted share of $0.01, and non-GAAP net income per diluted share of $0.74.

“In the quarter, we continued to experience strong adoption of our Vulnerability Management, Detection and Response (VMDR^®) application with paid Cloud Agent subscriptions growing approximately 58% year-over-year to 61 million deployed. As organizations continue to look for solutions to not only identify risk but also mitigate it quickly, we believe that VMDR is taking detection and response actions to the next level while setting a gold standard in the industry for security and compliance solutions. Given the power of VMDR to continuously detect vulnerabilities and misconfigurations across the entire global IT environment and respond in real time to remediate vulnerable or compromised assets from a single platform, adoption of our VMDR application continues to be a strategically important driver to our long-term growth,” said Sumedh Thakar, CEO of Qualys. “We are pleased with our strategic direction and remain confident that our innovative solutions, compelling value proposition, and strong market leadership position will lead to long-term value for our shareholders.”

First Quarter 2021 Financial Highlights

Revenues: Revenues for the first quarter of 2021 increased by 12% to $96.8 million compared to $86.3 million for the same quarter in 2020.

Gross Profit: GAAP gross profit for the first quarter of 2021 increased by 11% to $75.1 million compared to $67.8 million for the same quarter in 2020. GAAP gross margin was 78% for the first quarter of 2021 compared to 79% for the same quarter in 2020. Non-GAAP gross profit for the first quarter of 2021 increased by 11% to $77.6 million compared to $69.9 million for the same quarter in 2020. Non-GAAP gross margin was 80% for the first quarter of 2021 compared to 81% for the same quarter in 2020.

Operating Income (Loss): GAAP operating loss for the first quarter of 2021 was $2.7 million compared to GAAP operating income of $20.4 million for the same quarter in 2020, which primarily reflects an increase in stock-based compensation due to the accelerated vesting of the former CEO’s equity awards. As a percentage of revenues, GAAP operating income (loss) was negative 3% for the first quarter of 2021 compared to 24% for the same quarter in 2020. Non-GAAP operating income for the first quarter of 2021 increased by 16% to $37.1 million compared to $31.9 million for the same quarter in 2020. As a percentage of revenues, non-GAAP operating income was 38% for the first quarter of 2021 compared to 37% for the same quarter in 2020.

Net Income: GAAP net income for the first quarter of 2021 was $0.2 million, or $0.01 per diluted share, compared to $18.7 million, or $0.46 per diluted share, for the same quarter in 2020. The decrease in GAAP net income reflects the accelerated vesting of the former CEO’s equity awards, as described above. As a percentage of revenues, GAAP net income was 0% for the first quarter of 2021 compared to 22% for the same quarter in 2020. Non-GAAP net income for the first quarter of 2021 was $29.8 million, or $0.74 per diluted share, compared to non-GAAP net income of $26.6 million, or $0.65 per diluted share, for the same quarter in 2020. As a percentage of revenues, non-GAAP net income was 31% for both the first quarter of 2021 and the first quarter of 2020.

Adjusted EBITDA: Adjusted EBITDA (a non-GAAP financial measure) for the first quarter of 2021 increased by 17% to $44.6 million compared to $38.2 million for the same quarter in 2020. As a percentage of revenues, Adjusted EBITDA was 46% for the first quarter of 2021 compared to 44% for the same quarter in 2020.

Operating Cash Flow: Operating cash flow for the first quarter of 2021 increased by 10% to $57.9 million compared to $52.4 million for the same quarter in 2020. As a percentage of revenues, operating cash flow was 60% for the first quarter of 2021 compared to 61% for the same quarter in 2020.

First Quarter 2021 Business Highlights

Financial Performance Outlook

Based on information as of today, May 5, 2021, Qualys is issuing the following financial guidance for the second quarter and full year fiscal 2021. The Company emphasizes that the guidance is subject to various important cautionary factors referenced in the section entitled “Legal Notice Regarding Forward-Looking Statements” below, including risks and uncertainties associated with the COVID-19 pandemic.

Second Quarter 2021 Guidance: Management expects revenues for the second quarter of 2021 to be in the range of $98.6 million to $99.2 million, representing 11% to 12% growth over the same quarter in 2020. GAAP net income per diluted share is expected to be in the range of $0.37 to $0.39, which assumes an effective income tax rate of 31%. Non-GAAP net income per diluted share is expected to be in the range of $0.67 to $0.69, which assumes a non-GAAP effective income tax rate of 21%. Second quarter 2021 net income per diluted share estimates are based on approximately 40.3 million weighted average diluted shares outstanding for the quarter.

Full Year 2021 Guidance: Management now expects revenues for the full year of 2021 to be in the range of $402.5 million to $404.5 million, representing 11% growth over 2020, up from the previous guidance range of $399.0 million to $402.0 million. GAAP net income per diluted share is expected to be in the range of $1.06 to $1.11, down from the previous guidance range of $1.39 to $1.44. This assumes an effective income tax rate of 28%, up from the previous assumption of 26%. Non-GAAP net income per diluted share is expected to be in the range of $2.67 to $2.72, up from the previous guidance range of $2.60 to $2.65. This assumes a non-GAAP effective income tax rate of 21%. Full year 2021 net income per diluted share estimates are based on approximately 40.4 million weighted average diluted shares outstanding.

Investor Conference Call

Qualys will host a conference call and live webcast to discuss its first quarter 2021 financial results at 5:00 p.m. Eastern Time (2:00 p.m. Pacific Time) on Wednesday, May 5, 2021. To access the conference call, dial (877) 881-2609 in the U.S. or (970) 315-0463 for international participants with conference ID #4595838. A live webcast of the earnings conference call, investor presentation and prepared remarks can be accessed at https://investor.qualys.com/events-presentations. A replay of the conference call will be available through the same webcast link following the end of the call.

Investor Contact

Blair King

Vice President, Investor Relations and Corporate Development

(650) 801-6299

ir@qualys.com

About Qualys

Qualys, Inc. (NASDAQ: QLYS) is a pioneer and leading provider of disruptive cloud-based IT, security and compliance solutions with over 19,000 active customers in more than 130 countries, including a majority of each of the Forbes Global 100 and Fortune 100. Qualys helps organizations streamline and consolidate their security and compliance solutions in a single platform and build security into digital transformation initiatives for greater agility, better business outcomes, and substantial cost savings.

The Qualys Cloud Platform and its integrated Cloud Apps deliver businesses critical security intelligence continuously, enabling them to automate the full spectrum of auditing, compliance, and protection for IT systems and web applications across on premises, endpoints, cloud, containers, and mobile environments. Founded in 1999 as one of the first SaaS security companies, Qualys has established strategic partnerships with leading cloud providers like Amazon Web Services, Microsoft Azure and the Google Cloud Platform, and managed service providers and consulting organizations including Accenture, BT, Cognizant Technology Solutions, Deutsche Telekom, DXC Technology, Fujitsu, HCL Technologies, IBM, Infosys, NTT, Optiv, SecureWorks, Tata Communications, Verizon and Wipro. The company is also a founding member of the Cloud Security Alliance. For more information, please visit www.qualys.com.

Qualys, Qualys VMDR^® and the Qualys logo are proprietary trademarks of Qualys, Inc. All other products or names may be trademarks of their respective companies.

Legal Notice Regarding Forward-Looking Statements

This press release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Forward-looking statements generally relate to future events or our future financial or operating performance. Forward-looking statements in this press release include, but are not limited to, statements related to: our confidence that our solutions, value proposition and market leadership position will lead to long-term value for our shareholders; the benefits of our new and upcoming products, features, integrations, collaborations and joint solutions, and their impact upon our long-term growth; our guidance for revenues, GAAP EPS and non-GAAP EPS for the second quarter and full year 2021; and our expectations for the number of weighted average diluted shares outstanding and the GAAP and non-GAAP effective income tax rate for the second quarter and full year 2021. Our expectations and beliefs regarding these matters may not materialize, and actual results in future periods are subject to risks and uncertainties that could cause actual results to differ materially from those projected. These risks include our ability to continue to develop platform capabilities and solutions; the ability of our platform and solutions to perform as intended; customer acceptance and purchase of our existing solutions and new solutions; real or perceived defects, errors or vulnerabilities in our products or services; our ability to retain existing customers and generate new customers; the budgeting cycles and seasonal buying patterns of our customers; the length of our sales cycle; the impact of the ongoing COVID-19 pandemic and related public health measures on our business and the global economy; our ability to manage costs as we increase our customer base and the number of our platform solutions; the market for cloud solutions for IT security and compliance not increasing at the rate we expect; competition from other products and services; fluctuations in currency exchange rates; unexpected fluctuations in our effective income tax rate on a GAAP and non-GAAP basis; our ability to effectively manage our rapid growth and our ability to anticipate future market needs and opportunities; any unanticipated accounting charges; and general market, political, economic and business conditions in the United States as well as globally. The forward-looking statements contained in this press release are also subject to other risks and uncertainties, including those more fully described in our filings with the Securities and Exchange Commission, including our Quarterly Report on Form 10-Q for the quarter ended March 31, 2021, filed with the Securities and Exchange Commission on May 5, 2021.

The forward-looking statements in this press release are based on information available to Qualys as of the date hereof, and Qualys disclaims any obligation to update any forward-looking statements, except as required by law.

Non-GAAP Financial Measures

In addition to reporting financial results in accordance with GAAP, Qualys provides investors with certain non-GAAP financial measures, including non-GAAP gross profit, non-GAAP gross margin, non-GAAP operating expenses, non-GAAP operating income, non-GAAP net income, non-GAAP net income per diluted share, Adjusted EBITDA (defined as earnings before interest expense, interest income and other income (expense), net, income taxes, depreciation, amortization, and stock-based compensation) and non-GAAP free cash flows (defined as cash provided by operating activities less purchases of property and equipment (net of proceeds from disposal) and principal payments under finance lease obligations).

In computing non-GAAP financial measures, Qualys excludes the effects of stock-based compensation expense, and amortization of intangible assets from acquisitions. Qualys believes that these non-GAAP financial measures help illustrate underlying trends in its business that could otherwise be masked by the effect of the income or expenses, as well as the related tax effects, that are excluded in non-GAAP gross profit, non-GAAP gross margin, non-GAAP operating expenses, non-GAAP operating income, non-GAAP net income, non-GAAP net income per diluted share, Adjusted EBITDA and non-GAAP free cash flows.

Furthermore, Qualys uses some of these non-GAAP financial measures to establish budgets and operational goals for managing its business and evaluating its performance. Qualys believes that non-GAAP gross profit, non-GAAP gross margin, non-GAAP operating expenses, non-GAAP operating income, non-GAAP net income, non-GAAP net income per diluted share, Adjusted EBITDA and non-GAAP free cash flows provide additional tools for investors to use in comparing its recurring core business operating results over multiple periods with other companies in its industry.

Although Qualys does not focus on quarterly billings, Qualys provides calculated current billings (defined as total revenues recognized in a period plus the sequential change in current deferred revenue in the corresponding period) to assist investors and analysts in assessing its operating performance.

Qualys has not reconciled non-GAAP net income per diluted share guidance to GAAP net income per diluted share guidance because Qualys does not provide guidance on the various reconciling cash and non-cash items between GAAP net income and non-GAAP net income (i.e., stock-based compensation and amortization of intangible assets from acquisitions). The actual dollar amount of reconciling items in the second quarter and full year 2021 is likely to have a significant impact on the Company’s GAAP net income per diluted share in the second quarter and full year 2021. A reconciliation of the non-GAAP net income per diluted share guidance to the GAAP net income per diluted share guidance is not available without unreasonable effort.

In order to provide a more complete picture of recurring core operating business results, the Company’s non-GAAP net income and non-GAAP net income per diluted share include tax adjustments required to achieve the effective income tax rate on a non-GAAP basis, which could differ from the GAAP effective income tax rate. The Company believes its estimated non-GAAP effective income tax rate of 21% in 2021 is a reasonable estimate under its global operating structure. The Company may adjust this rate during the year to take into account events or trends that it believes materially impact the estimated annual rate. The non-GAAP effective income tax rate could be subject to change for a number of reasons, including but not limited to, significant changes resulting from tax legislation, material changes in geographic mix of revenues and expenses and other significant events.

The presentation of this non-GAAP financial information is not intended to be considered in isolation or as a substitute for results prepared in accordance with GAAP. A reconciliation of the non-GAAP financial measures discussed in this press release to the most directly comparable GAAP financial measures is included with the financial statements contained in this press release. Management uses both GAAP and non-GAAP information in evaluating and operating its business internally and as such has determined that it is important to provide this information to investors.

Qualys, Inc.

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS

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RECONCILIATION OF NON-GAAP DISCLOSURES

ADJUSTED EBITDA

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