Nessus is a free, up-to-date, and full featured remote security scanner for Linux, BSD, Solaris and some other systems. It is multithreaded, plugin-based, has a nice GTK interface, and currently performs over 320 remote security checks. It has powerful reporting capabilities (HTML, LaTeX, ASCII text) and not only points out problems, but suggests a solution for each of them.
You can download it from the following link: https://packetstormsecurity.com/files/download/10446/nessus-0.99.5-1.tgz
Source: https://packetstormsecurity.com/files/10446/nessus-0.99.5-1.tgz.html