Virtual Private Network
A Virtual Private Network (VPN) is a computer networking technique which connects remote computers through an insecure network to a local area network, as if that computer was connected locally. The VPN-linked computer can then communicate as freely as any other computer on the LAN. VPNs are sometimes used for industrial and commercial networks, when employees must connect to the company network from outside of the building. Although the communication is passing through an insecure network, the data stream is encrypted, so it cannot be easily compromised.
VPNs are also sometimes used for privacy. In this case, remote computers connect through an encrypted tunnel to a host. From there, the outgoing packets are sent to the destination. That destination device then responds, but not directly to the client. Rather, the response is sent to the VPN, from which it is passed on the client. In this way, the remote server never knows the client's IP address, the client's Internet provider does not know what data is being exchanged, and anyone else attempting to tap into the client's communications will have the same difficulty. Although not impenetrable, this is method does offer significant privacy and security, if used properly.
VPN's work by utilising a type of encryption called RSA public key encryption.