Xshell supports TCP/IP and X11 forwarding feature which creates a secure tunnel between your PC and another machine across an untrustworthy network.
For example, you are at home and want to retrieve your e-mail from the server at work with a POP3 client program. If you connect to the server directly, your e-mail client sends your login and password information as plain text. This means that your important account information could be tapped and stolen by malicious users.
To prevent this, you can use the SSH tunneling feature provided by Xshell. Xshell establishes a secure tunnel between your PC at home and the mail server at work. Then the POP3 client connects to Xshell at your local PC rather than connecting to the remote mail server directly. Xshell forwards all traffics to the mail server over the secure tunnel and transfers all traffics received from the mail server to the POP3 client. This is called a port forwarding mechanism.