(Secure SHell) A security protocol for logging into a remote server. SSH provides an encrypted session for transferring files and executing server programs. Also serving as a secure client/server connection for applications such as database access and e-mail, SSH supports a variety of authentication methods.

SSH was developed in the mid-1990s by Helsinki University researcher Tatu Ylönen as a secure alternative to non-secure telnet, rlogin and rsh programs for Unix servers. SSH-2, a more advanced version introduced in 1998, was standardized by the IETF and is not compatible with SSH-1.

Secure File Transfer: SFTP and SCP
SSH File Transfer Program (SFTP) was developed by the IETF for transferring files with SSH-2. Secure Copy Protocol (SCP) is a version of the Unix remote copy (rcp) command that is widely supported on Unix systems running SSH-1.

All Platforms - Free and Paid
SSH is widely used on all platforms, and software is available as open source from the OpenSSH group (www.openssh.org) and numerous commercial vendors, including SSH Communications Security Corporation (www.ssh.com), the company founded by Ylönen. See FTPS.