Stuxnet virus

Stuxnet is a computer worm discovered in June 2010. It initially spreads via Microsoft Windows, and targets Siemens industrial software and equipment. While it is not the first time that hackers have targeted industrial systems, it is the first discovered malware that spies on and subverts industrial systems, and the first to include a programmable logic controller (PLC) rootkit.

[Iranian engineers have succeeded in neutralizing and purging the computer virus known as Stuxnet from their country's nuclear machinery, European and U.S. officials and private experts have told Reuters.
The malicious code, whose precise origin and authorship remain unconfirmed, made its way as early as 2009 into equipment controlling centrifuges Iran is using to enrich uranium, dealing a significant but perhaps temporary setback to Iran's suspected nuclear weapons work. - 15/02]

Experts believe that Stuxnet required the largest and costliest development effort in malware history.[23] Its many capabilities would have required a team of people to program, in-depth knowledge of industrial processes, and an interest in attacking industrial infrastructure.[2][7] Eric Byres, who has years of experience maintaining and troubleshooting Siemens systems, told Wired that writing the code would have taken many man-months, if not years.

The worm worked by first causing an infected Iranian IR-1 centrifuge to increase from its normal operating speed of 1,064 hertz to 1,410 hertz for 15 minutes before returning to its normal frequency. Twenty-seven days later, the worm went back into action, slowing the infected centrifuges down to a few hundred hertz for a full 50 minutes. The stresses from the excessive, then slower speeds, caused the aluminum centrifugal tubes to expand, often forcing parts of the centrifuges into sufficient contact with each other to destroy the machine.[70]

According to the Washington Post, International Atomic Energy Agency (IAEA) cameras installed in the Natanz facility recorded the sudden dismantling and removal of approximately 900–1000 centrifuges during the time the Stuxnet worm was reportedly active at the plant. Iranian technicians, however, were able to quickly replace the centrifuges and the report concluded that uranium enrichment was likely only briefly disrupted.