PeerGuardian is a free and open-source software that allows users to block incoming and outgoing connections from IP addresses that are known to be associated with undesirable activity. The software uses regularly updated blocklists to protect users from known threats such as spyware, adware, and government surveillance. PeerGuardian also includes the ability to customize blocklists and whitelist trusted IP addresses. Additionally, the software has a user-friendly interface and is compatible with multiple operating systems.