TOR, short for "The Onion Router," is a worldwide network of servers that are used to help anonymize people's Web surfing. Web traffic is randomly routed through many servers, masking critical information such as someone's true IP (Internet Protocol) address.

TOR is often used by people who want to enhance their privacy while surfing the Internet, as IP addresses are an important piece of information to collect when monitoring Internet traffic.

Web sites will record the IP address of the last exit point out of the TOR network, which could make it appear users have an IP address from a Brazilian ISP when they are actually in Germany.

The attack did not appear to be specifically aimed at disrupting TOR or compromising people's privacy, wroteRoger Dingledine, the project's director. Two of the seven directory authorities, which hold a list of nodes in the TOR network, were hacked along with another server that recorded statistics about TOR.