PRESS RELEASE

Columbia, MD – April 4, 2013 – Tenable Network Security, Inc., the leader in real-time vulnerability management, celebrates the 15th anniversary of Nessus®, the world's most widely deployed vulnerability scanner. With more than 17,000 customers in over 140 countries, the world's largest organizations, including the entire U.S. Department of Defense, Merck, Morgan Stanley, and Verizon, use Nessus to scan defense systems, power and utility plant control systems, healthcare information systems, and financial services infrastructures.

Shown in a timeline highlighting some of the major milestones over the past 15 years, Nessus was launched on the Linux operating system (OS) on April 4, 1998, by Renaud Deraison, Tenable's CRO and co-founder. The initial release of Nessus was capable of checking for 50 vulnerabilities. Today, running on Windows, Mac, FreeBSD, Solaris, and a variety of Linux-based OSes or from our cloud service, Nessus scans more OSes, applications, and network infrastructures than any other solution. Nessus checks for more than 54,000 vulnerabilities, assesses secure configuration settings, and performs compliance auditing against more than 450 devices and applications. Keeping pace with changing technologies, Nessus can scan everything from mainframes to cloud applications and mobile and virtual devices. Most recently Nessus has been enhanced with technology that finds malware and botnets that evade most antivirus vendors.

Following the product's 10-year anniversary, Nessus continued expanding and gained significant recognition as it was named one of SC Magazine's "Top 20 Products" of the last 20 years in 2009, reached 15,000 Nessus and SecurityCenter&trade customers worldwide in 2012, and surpassed 10,000,000 downloads and 54,000 plugins in 2013.

"Since its origins 15 years ago, Nessus has been a crucial tool for security professionals worldwide and provides a tremendous value," said Ron Gula, CEO and co-founder of Tenable Network Security. "The amazing capability to remain ahead of security concerns and compliance needs for more than a decade is truly remarkable and is a tribute to the expert engineering and forward-looking development begun by Renaud and continued by Tenable's talented group of software engineers."

Tenable Network Security is one of the most recognized cybersecurity companies in the world, providing protection to numerous organizations including the U.S. Department of Defense. Along with Nessus, its SecurityCenter platform is the first to provide real-time detection and notifications of vulnerabilities within networks that can be exploited by hackers. Tenable's products are used by enterprises, governments, and military entities around the world to provide top-tier vulnerability management for critical systems and information.

To learn more about Nessus and its accomplishments, please visit www.tenable.com/nessus-15.

For more information on Tenable Network Security products and solutions, please visit www.tenable.com.

About Tenable Network Security

Tenable Network Security is relied on by more than 17,000 organizations, including the entire U.S. Department of Defense and many of the world's largest companies and governments, to stay ahead of emerging vulnerabilities, threats and compliance-related risks. Its Nessus and SecurityCenter solutions continue to set the standard for identifying vulnerabilities, preventing attacks and complying with a multitude of regulatory requirements. For more information, please visit www.tenable.com.