As the worm turns ~ malevolent software hits Iran  By Dan Yurman
In July 2010 a software worm, which is malevolent computer code,
appeared on the radar screen of cyber security firms when it was
found to be targeting computers in Iran and several other
countries running industrial control systems.  News reports in
the mainstream and computer trade press suggested that the
Stuxnet worm was designed to sabotage the Russian-built
commercial nuclear power station at Bushehr in Iran and some or
all of Iran’s secret and not-so-secret uranium enrichment
plants.  German computer security expert Ralph Langer was among
the first to report that the worm attacked software used to run
a specific model of a Programmable Logic Controller (PLC) made
by Siemens. The specific PLC targeted by the Stuxnet worm is the
Siemens SIMATIC WinCC/Step 7 controller and its software.
Langer speculated that the Stuxnet worm was designed to disable
PLCs installed at nuclear facilities in Iran because those
facilities used so many of them.