Screaming Penguin - Source Does Matter

openSSH is the open source implementation of the Secure SHell. A secure shell is a means of logging into a machine, generally remotely, and having the session "secure"d via encryption. openSSH currently supports the SSH protocols 1.3, 1.5 and 2.0 (in the latest rev which is openSSH 2.0.)

openSSH also does a lot more than encryption. The additional features include X11 forwarding, port forwarding, Kerberos forwarding and more. openSSH props go to the original developers (Tatu Ylonen and then Bjorn Gronvall) and to the openBSD dev team who thought that all of this should be great open source stuff. openSSH in its current form comes to all via openBSD, thanks.

The linked installation and configuration tutorial by SysAdmin is very good, and this is a must have on every UNIX box (no more telnet.) Also though it is less frequently mentioned there is a brethren program called scp, or secure copy that comes with openSSH and it allows for secure file transfer (replacement for ftp.)

You must of course have a configured server to login to, and a client to use SSH. The links also contain a site called freeSSH which is a great reference for all things SSH including GUI clients (yes, even for that windoze box.)

Checkit all via the links, and security now! (yes, a Seinfeld reference, sorry about that.)   Installing and Configuring openSSH: SysAdmin