Stuxnet worm was planted by inside man
According to a report by Industrial Safety and Security Source (ISS Source), which cites US intelligence sources, Israel's foreign intelligence agency Mossad used a worker at Iran's Natanz uranium enrichment facility to infiltrate the Stuxnet worm into the facility. The officials told the news site that the worker was of Iranian origin and used a specially crafted USB flash drive to load the malware onto the Natanz systems. The worker is said to have probably belonged to an opposition group.
Mossad is also reported to have used double agents to identify weak points in the facility in order to improve its chances of success. The report says that these agents were probably members of the militant Iranian opposition movement Mujahideen-e Khalq (MEK).
In the summer of 2010, Stuxnet made headlines because it exploited previously unknown security vulnerabilities in Windows, was signed with a valid certificate, and appears to have been specially developed to attack the uranium enrichment facility in Natanz.