Tor Browser Bundle - Tor, Vidalia, Torbutton, Polipo and Firefox 0.2.1.21 for Windows 7, Windows Vista, Windows XP
Tor is free software and an open network that helps you defend against a form of network surveillance that threatens personal freedom and privacy, confidential business activities and relationships, and state security known as traffic analysis.
Tor protects you by bouncing your communications around a distributed network of relays run by volunteers all around the world: it prevents somebody watching your Internet connection from learning what sites you visit, and it prevents the sites you visit from learning your physical location. Tor works with many of your existing applications, including web browsers, instant messaging clients, remote login, and other applications based on the TCP protocol.
Hundreds of thousands of people around the world use Tor for a wide variety of reasons: journalists and bloggers, human rights workers, law enforcement officers, soldiers, corporations, citizens of repressive regimes, and just ordinary citizens.