http://www.jpost.com/IranianThreat/News/Article.aspx?id=199475

The Stuxnet virus, which has attacked Iran’s nuclear facilities and which Israel is suspected of creating, has set back the Islamic Republic’s nuclear program by two years, a top German computer consultant who was one of the first experts to analyze the program’s code told The Jerusalem Post on Tuesday.

Maybe a bit optimistic, but it sure has had a big effect and was as effective and pinpointed as an Israeli Air Force strike. Usually viruses attack very indiscriminately, and usually target the most common operating systems on PCs. This virus is very unique.
The success of this operation is so complete that many more will come.