Metasploit :
Some times Hackers are hired for penetration testing of a website. The Hackers hack the websites and they find out the loop holes. Hackers can't hack anything without tools or softweres. They always need many kind of tools and softweres for everything like penetration testing, cracking, decrypting, for breaking firewalls etc. Metasploit is a community who provide the Hackers these tools and softweres. This is not illegal. You can use their tools and softweres as a White Hat Hacker.
Please don't misuse this information. This is only for increasing knowledges.