"Is a Cyber Attack Targeting Iran's Nuclear Plant?"

"This is the first direct example of weaponized software, highly customized and designed to find a particular target," said Michael Assante, former chief of industrial control systems cyber security research at the U.S. Department of Energy's Idaho National Laboratory.

Stuxnet targets industrial control systems, such as those that power Iran's Bushehr nuclear plant. And some experts speculate that it was written by a nation explicitly to take out Bushehr.