What is "peerguardian"

PeerGuardian is a free and open source program developed by Phoenix Labs. It is capable of blocking incoming and outgoing connections based on IP blacklists. The system is also capable of blocking custom ranges, depending upon user preferences.

The Windows version of this program has been discontinued in favor of other applications (Phoenix Labs encourage current PeerGuardian users to migrate to PeerBlock which is based on PeerGuardian 2).