It has been discovered that the operating system at the Bushehr plant, Iran's first nuclear power station, has been infested with the Stuxnet worm. The worm is a highly complex, malicious software ( weapon ) that focuses on the vulnerabilities of systems built by the Siemens company. The Stuxnet worm is capable of seizing control of industrial plants, and it's complexity suggests that it must have been built by a nation-state.
It is estimated that the Stuxnet worm has infected up to 30,000 IP addresses in Iran, and it has been found on the personal computers of staff of the plant.