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 330 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/17636/nessus-1.0.0pre2.tar.gz
Source: https://packetstormsecurity.com/files/17636/nessus-1.0.0pre2.tar.gz.html