PeerGuardian is software that can be used to block connections from IP addresses that are associated with known malicious or undesirable activity, such as government agencies, corporations, and spammers. The software is designed to protect users from potential threats while using peer-to-peer (P2P) file sharing networks. The main features of PeerGuardian include automatic updates of blocklists, the ability to customize blocklists, and easy-to-use interface.