Most experts think the virus was somehow introduced into Iran's control systems via some kind of computer thumb drive.European and US experts have said that they believe that Stuxnet, at least for a time, caused serious malfunctions in the operations of Iranian nuclear centrifuges.Iran and its antagonists today appear to be engaged in multiple levels of clandestine warfare, with unknown assailants killing Iranian nuclear scientists and, in the last few days, bomb attacks on Israeli embassy personnel in India and Georgia. Israel has blamed Iran.