A popular protocol for tunneling traffic through a firewall. There are two popular version. V4 is the most popular version. V5 adds authentication and encryption.
SOCKS is a firewall tunneling service. It allows many machines behind a firewall to access the Internet without actually being on the Internet themselves.
In theory, SOCKS should only be visible from the internal side of the server, but not from the Internet. Hackers will frequently probe to see if SOCKS is visible from the other side. If that is the case, they can attack your internal network, or almost as bad, launch attacks on other Internet sites from your machine.
