Siemens told German daily Süddeutsche Zeitung that 15 of its customers had been affected – including chemical and power plants and production facilities. The company said operators reported the problem to Siemens after discovering the cyber worm in their systems.
Five of the 15 companies affected have their headquarters in Germany, while the others are based in the United States, Asia and other Western European countries.
After operators discovered the Stuxnet worm, Siemens assisted each one of them in deleting the virus. Siemens said the operators retained control of their facilities and no shutdown was required.
Experts consider the Stuxnet virus to be the "first cyber super weapon." It is capable of breaking into computers that control machinery at the heart of industry, allowing an attacker to assume control of critical systems like pumps, motors, alarms and valves.
It could, technically, make factory boilers explode, destroy gas pipelines or even cause a nuclear plant to malfunction.
Stuxnet is believed to target Siemens control systems, which are commonly used to manage water supplies, oil rigs, power plants and other industrial facilities.
The company said they succeeded in isolating the virus at a test facility for further study. "Our analyses have not yielded any conclusions on the specific purpose or the maker of the virus," Siemens told Süddeutsche Zeitung.
The computer worm – a piece of malicious software (malware) which copies itself and sends itself on to other computers in a network – was first spotted by Siemens on July 15, a company spokesman told AFP.