FOR Iran’s beleaguered opposition, the internet is a potent weapon and a big hope. During the Green movement’s protests in 2009, activists used Twitter and Facebook, often from mobile phones, to upload videos of police brutality and spread messages of support and news of new demonstrations. The authorities responded not only by cracking heads, but cracking computers: trying to trace users, block services and close websites. Outsiders found the struggle inspirational. Austin Heap, a 26-year-old hacker born in Ohio, decided to develop anticensorship software to foil the authorities’ efforts. He named the product Haystack, and began earlier this year to...