VPN is a wide area network of connected LANs. The LANs are connected through Internet .

The network is a private network, but use Internet as the medium for transporting data. These systems use encryption and other security mechanisms to ensure that only authorized users can access the network and that the data cannot be intercepted.

VPN Security
A VPN is designed to provides a secure, encrypted tunnel in which to transmit the data between the remote user and the company network.  The first step to security is usually a firewall between the client and the host server, requiring the remote user to establish an authenticated connection with the firewall.