The Nessus® vulnerability scanner is the world-leader in active scanners with more than five million downloads to date. Nessus features high-speed discovery, configuration auditing, asset profiling, sensitive data discovery and vulnerability analysis of your security posture. Nessus scanners can be distributed throughout an entire enterprise, inside DMZs and across physically separate networks.
How to Install (Ubuntu): http://linhost.info/2009/03/nessus-installation-on-ubuntu/
Run Nessus Server: /etc/init.d/nessusd start
Run Nessus Client: 127.0.0.1:8834 in browser
Stored Folder: /opt/nessus/