A German security expert interviewed by the Jerusalem Post claims the Stuxnet virus was apparently as effective as a real military strike. The expert, identified only as "Langer", estimates the virus set back the Iranian nuclear program by as much as two years.
Speaking to the Post, an expert identifed only as "Langer" (we believe the Post likely means Stuxnet expert Ralph Langner, but have not had confirmation at the time of writing) said that due to poor Iranian IT security expertise, the only effective way the country would be able to rid itself of the virus would be through discarding all infected machines. He said that, further, centrifuges would need to be replaced at Iran's Natanz facility, as might a turbine at Bushehr. Centrifuges operating at between 807Hz and 1210Hz were believed to be a specific target of the virus.
Even if the Iranians can clean up their own machines—whether by replacing them entirely or removing the virus—the country will have to ensure that outside contractors remain uninfected too.