When Iranian protesters used internet services like Twitter to gain global attention they also reminded the world that oppressive regimes continue to buy or build technologies to enforce censorship.

Clothilde Le Coz, director of internet research for Reporters Without Borders, says Iran is second only to China in the extent and sophistication of its efforts to stifle dissent online.

“The Iranian government said last year that it was blocking 5 million websites,” Le Coz said in a telephone interview. “They brag about what they can do, perhaps to intimidate their opponents.”