What is "peerblock"

PeerBlock is a free and open-source personal firewall. PeerBlock is the successor to PeerGuardian (which is only actively maintained in Linux). It blocks incoming and outgoing connections to Internet IP addresses that are included on blacklists accessible over the Internet which may be selected by the user, and to addresses specified by the user. PeerBlock mainly uses blocklists provided by iblocklist.com. While the software is free, a subscription must be paid for access to lists of sites to block.