Bot Revolt blocks "known bad" computers from accessing yours, and vice versa. Depending on the lists you have it setup to use, you can block governments, corporations, machines flagged for anti-p2p activities, even entire countries! Whether you're sharing files or just surfing the web, Bot Revolt can help protect you from the bad guys. Bot Revolt stops hackers and botnets from stealing your data. More powerful than a firewall, Bot Revolt blocks over 1 Billion malicious IPs.
Bot Revolt is a type of program known as an "IP Filter" and extra layer of security. It lives way down deep inside the networking code on your computer - the stuff in Windows that actually makes/receives network connections for you - and inspects everything that flows past it. It looks at the IP address this network "packet" is coming from, and compares it against a list of "bad" ip-addresses; if it finds a match, it doesn't let that network packet make it through to the rest of your computer. It also looks at the IP address your network packets are going to, and does the same thing.
Bot Revolt is based of PeerBlock. (http://www.peerblock.com)