Nessus (software)
In computer security, Nessus is a proprietary comprehensive vulnerability scanning program. It is free of charge for personal use in a non-enterprise environment. Its goal is to detect potential vulnerabilities on the tested systems.
According to surveys done by sectools.org, Nessus is the world's most popular vulnerability scanner, taking first place in the 2000, 2003, and 2006 security tools survey. Tenable estimates that it is used by over 75,000 organizations worldwide.