A highly sophisticated computer worm that has spread through Iran, Indonesia and India was built to destroy operations at one target: possibly Iran's Bushehr nuclear reactor.That's the emerging consensus of security experts who have examined the Stuxnet worm. In recent weeks, they have broken the cryptographic code behind the software and taken a look at how the worm operates in test environments. Researchers studying the worm all agree that Stuxnet was built by a very sophisticated and capable attacker -- possibly a nation-state -- and it was designed to destroy something big.Though it was first developed more than a year ago, Stuxnet was discovered in July 2010, when a Belarus-based security company found the worm on computers belonging to an Iranian client. Since then it has been the subject of ongoing study by security researchers, who say they have never seen anything like it before. Now, after months of private speculation, some of the researchers who know Stuxnet best say that it may have been built to sabotage Iran's nukes.