The Stuxnet Worm

Ars reported Stuxnet worm attacks industrial targets, could be aimed at Iran "Security researchers have uncovered some unexpected behaviors in a piece of malware called Stuxnet. The worm exploits a number of zero-day vulnerabilities in order to propagate itself over Windows networks, but it also targets embedded software developed by Siemens that runs in industrial equipment. The worm could be used to disrupt factories and other industrial environments. Researchers have found that the highest concentration of Stuxnet infections is located in Iran. That discovery, coupled with the very high level of sophistication exhibited by the malware, has led some researchers to speculate that it was crafted by a major government body with the aim of disabling Iran's nuclear power plant."

Here's Schneier on The Stuxnet Worm.