I saw this article recently that talks about the Stuxnet worm in Iran. It apparently is targeting SCADA systems and possibly may have been written to specifically target nuclear systems, although Iran denies claims that its nuclear systems have been affected.
The worm was designed to attack Siemens SCADA systems, and recent speculations indicate that it was likely developed by a private group, and it would’ve taken months to code and test it. It is the first worm to ever include a PLC rootkit. Many have posited that only a nation state would have developed this (source 1, source 2), and the finger has been pointed at Israel, the United States, and even at NATO.
Cyber warfare anyone?