Tor: An anonymous Internet communication system

Tor is a toolset for a wide range of organizations and people that want to improve their safety and security on the Internet. ItUsing Tor can help you anonymize web browsing and publishing, instant messaging, IRC, SSH, and more. Tor also provides a platform on which software developers can build new applications with built-in anonymity, safety, and privacy features.

Your traffic is safer when you use Tor, because communications are bounced around a distributed network of servers, called onion routers. Instead of taking a direct route from source to destination, data packets on the Tor network take a random pathway through several servers that cover your tracks so no observer at any single point can tell where the data came from or where it's going. This makes it hard for recipients, observers, and even the onion routers themselves to figure out who and where you are. Tor's technology aims to provide Internet users with protection against "traffic analysis," a form of network surveillance that threatens personal anonymity and privacy, confidential business activities and relationships, and state security.

You can see how it works in Electronic Frontier Foundation's web.

And you can download it.