It's hard to get good information about Iran's Internet censorship efforts, because anyone who probes the system from the inside risks consequences. But two psuedononymous Iranians working in collaboration with J. Alex Halderman of the University of Michigan have published a paper walking readers through basics of the country's censorship regime. 

One of the most interesting bits from the paper is a chart showing which categories of website get blocked. 

Via "Internet Censorship in Iran: A First Look"Via "Internet Censorship in Iran: A First Look"

A lot of what's blocked, not surprisingly, is porn. But there's a fairly high amount of censorship in the News, Art, Society, and Top 500 categories too. 

Who decides what gets censored? It's pretty complicated. As the paper explains, "the administrative hierarchy of Internet censorship in Iran is complex and includes many players." But the country is working on centralizing the process. Last year it created the Supreme Council of Cyberspace, which, in addition to sounding extremely impressive, controls three bodies that decide and enforce what's off limits. 

The Committee for Determining Offensive Contents "controls censorship policies in Iran," according to the paper. Basically this committee keeps updated lists of no-go sites and enforce related communications regulations.

The Iran Cyber Police, meanwhile, are are "responsible for prosecuting users who are involved in illegal Internet activities as described by the Committee for Determining Offensive Contents."

And then there's the Revolutionary Guard Cyber Defense Command, which is also known as the Iran Cyber Army, which manages the country's cybersecurity, detecting and protecting against outside threats. 

(H/T to Tim Lee at The Washington Post's excellent new tech blog, The Switch, for pointing out the paper.)