The best VPN must include
.-The Confidentiality (Privacy) is a certification that the information as confidential, and will only have the right to access that information. In order to prevent anyone who is in the middle of the Internet (the Man in the middle) to read or intercept information
.-Authentication is the process that verifies the proof to show that a person who has been granted. Not active Attacker to sneak
-For more information, see Data integrity is not changed during the delivery, especially to send across the Internet.
.-The middle Man in the Anti-replay protection secretly stored Packet that originates from the communication and change or edit the stored Packet then drop back into the Network based on the original.