High Quality Content by WIKIPEDIA articles! PeerBlock is a free software firewall application. 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 blocklists accessible over the Internet which may be selected by the user, but also any addresses manually specified by the user. PeerBlock mainly works in tandem with the blocklist provider iblocklist.com.