Tor and I2P are the most popular low-latency anonymous communication networks, which use the onion routing technique to protect user anonymity. The use of Tor or I2P within a company can create network security risks. These two anonymous networks are different in a number of technical details, some of which are operated by hackers. In this paper a comparison of The Onion Router and the Invisible Internet Project “Tor vs I2P” is presented, in order to find a solution to detect the use of this kind of communication. Both networks will be contrasted and compared in their most important aspects namely node selection, performance and scalability. The detailed comparison of the two systems will allow us to develop a solution to detect the use of the anonymous “Tor & I2P” network by implementing their signatures in a Snort intrusion detection system with newly designed rules.