Porn is highly illegal in Iran, and sites containing erotic material are blocked at the ISP-level as a matter of routine. These efforts to stamp out smut are usually contained within the country’s borders. But last Thursday, something weird happened.

According to The Verge, 256 porn sites – many with names like superbigcocks.com – started to gradually disappear from the Internet. While the servers themselves were working fine, users as far away as Russia and Hong Kong were getting nothing but blank players.

The culprit? Iran’s biggest ISP, The Telecommunication Company of Iran (TCI).

Here’s what happened. The TCI had announced fraudulent routes to the IP addresses for the 256 sites. These phony routes were then blindly adopted by ISPs in places as disparate as Russia, India, Indonesia and Hong Kong.

This devious trick is known as BGP hijacking, and is the Internet equivalent of giving fake directions when someone pulls up beside you in their car.

After 28 hours, this issue started to resolve itself, with most of the networks affected having revoked the phony routes. But within Iran, these routes continue to circulate.

BGP hijacking isn’t a common tool used for Internet censorship, largely due to the fact that it’s extremely noisy, easily mitigated against, and has the potential to spread past a country’s borders. That said, it’s not entirely unheard of.

In 2008, Pakistan’s government used the technique to block access to YouTube within the country, inadvertently blocking the site worldwide. And in 2010, China Telecom used BGP hijacking to route 15 percent of the Internet though the country, where it wouldn’t have been otherwise.

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