Eugene Kaspersky, CEO of Kasperky security firm revealed that a staffer at the unnamed nuclear Russian plant informed him of the infection. Stuxnet is widely considered to have been developed by the US Government in a joint work with Israel cyber units as a means to disrupt Irans nuclear enrichment plans. The virus infected the internal network of a Russian nuclear plant, exactly in the same way it compromised the control system in Iranian nuclear facilities in Natanz, to spread the malware attackers used as attack vector.”]
Source: http://securityaffairs.co/wordpress/19604/malware/stuxnet-russian-nuclear-facility.html