Install and configure Nessus Vulnerability Scanner on CentOS 7 and Ubuntu 15.10/15.04

Nessus is an Open Source remote security scanning tool, which scans a computer and raises an alert if it discovers any vulnerabilities that malicious hackers could use to gain access to any computer you have connected to a network. It does this by running over 1200 checks on a given computer, testing to see if any of these attacks could be used to break into the computer or otherwise harm it.