The virus creates malicious software that can be used for espionage and sabotage.
Siemens told that the malware is a Trojan worm dubbed Stuxnet that spreads via infected USB thumb drives, exploiting a yet-to-be-patched vulnerability in Microsoft Corp's Windows operating system.
The problem was first reported in Wednesday, Jul 14 2010.
"Just viewing the contents of the USB stick can activate the Trojan. Siemens recommends avoiding the use of a USB stick," said Siemens spokesman Alexander Machowetz.
Once the worm infects a Siemens system, it quickly sets up communications with a remote server computer that can be used to steal proprietary corporate data or take control of the Supervisory Control and Data Acquisition (SCADA) system.
Analysts explained that the attackers may have chosen to spread the malicious software via a thumb drive because many SCADA systems are not connected to the Internet, but do sport USB ports.