PPTP

The oldest and one of the most widely used VPN protocols, its major benefit is that it works on nearly every major operating system. PPTP stands for Point-To-Point Tunneling Protocol and that is exactly what it does. It creates a point-to-point connection to privately “tunnel” information over the internet. Unfortunately, the security of this protocol has been called into question of late because of several known security issues.

Resources
[1] "What is a VPN?". WhatIsMyIPAddress.com. Retrieved 2017-03-31.