Nessus

Nessus is a vulnerability scanner which is developed by Tenable Network Security. It is free of charge for personal use in a non-enterprise environment.

According to surveys done in 2009 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 Network Security estimated year 2005 that it was used by over 75,000 organizations worldwide.

Nessus allows scans for the following types of vulnerabilities:

• Vulnerabilities that allow a remote hacker to control or access sensitive data on a system.
• Misconfiguration (e.g. open mail relay, missing patches, etc.).
• Default passwords, a few common passwords, and blank/absent passwords on some system accounts. Nessus can also call Hydra (an external tool) to launch a dictionary attack.
• Denials of service against the TCP/IP stack by using malformed packets
• Preparation for PCI DSS audits