Examining How the Great Firewall Discovers Hidden Circumvention Servers
Roya Ensafi, David A. Fifield, Philipp Winter, Nick Feamster, Nicholas C. Weaver, Vern Paxson · 2015
Recently, the operators of the national censorship infrastructure of China began to employ "active probing" to detect and block the use of privacy tools. This probing works by passively monitoring the network for suspicious traffic, then actively probing the corresponding servers, and blocking any that are determined to run circumvention servers such as Tor.