The Onion Router
Tor (The Onion Router) is an implementation of second-generation onion routing.
Tor is a distributed censorship-resistant network designed to anonymize TCP-based applications.
Eavesdropping by exit nodes
Tor doesn't encrypt traffic between an exit node and the target server, so exit nodes are able to capture all unencrypted traffic. Malicious exit nodes can perform man-in-the-middle attacks on encrypted protocols.