In 2010, Iran reported that as many as 1,000 of its centrifuges at the Natanz nuclear facility, used for enriching weapons-grade uranium, were destroyed by a computer virus. The virus allegedly wrecked the electric motors by accelerating them to damaging speeds and setting back the Iranian nuclear program for at least two years. Iran blamed the U.S. and Israeli intelligence agencies for the attack.
According to the Washington-based Institute for Science and International Security, the weapon used for the attack was probably a virus called Stuxnet. But unlike other computer viruses, Stuxnet is designed to attack only networks with specific configurations.
Stuxnet is a type of computer program called a "worm" that can be inserted into a computer or a network of computers, where it replicates itself infecting other machines. Once inside a computer, a worm can corrupt or damage files, causing malfunction of programs.
Stuxnet is designed to attack computers with Microsoft Windows operating systems, and it can be most easily inserted through infected removable drives - pocket-size memory banks that connect to standard USB ports.
After the damage is done, Stuxnet is designed to self-destruct so it is very hard to trace. According to experts studying Stuxnet, it is a very complex program and only government agencies are capable of designing it.