Iran's nuclear programme is under the spotlight again this week; diplomats from the five permanent members of the security council plus Germany are in Istanbul for talks with Saeed Jalili, Iran's chief nuclear negotiator. Iran is under pressure to prove that its nuclear activities are peaceful. The US has warned of more sanctions if the government does not cooperate. But behind the scenes, US and Israeli officials are surprisingly upbeat about the issue. That is because it is widely believed that Iran's nuclear programme has been put back by several years after a computer virus damaged a number of its centrifuges. But who is behind the Stuxnet worm? Inside Story, with presenter Shiulie Gosh, discusses.