The problem with creating Stuxnet, the world's most sophisticated malware worm, is that it could eventually go rogue. Which is precisely what has happened. The US- and Israeli-built virus has spread to a Russian nuclear plant — and even the International Space Station.
Stuxnet is an incredibly powerful computer worm that was created by the United States and Israel to attack Iran's nuclear facilities. It initially spreads through Microsoft Windows and targets Siemens industrial control systems. It's considered the first malware that both spies and subverts industrial systems. It's even got a programmable logic controller rootkit for the automation of electromechanical processes.
Let that last point sink in for just a second. This thing, with a little bit of coaxing, can actually control the operation of machines and computers it infects.
For more on Stuxnet, I highly encourage you to watch this sobering TED talk by Ralph Lagner where he describes it as "a 21st century cyber weapon."

This thing is seriously badass, and now it's on the loose. Speaking to journalists in Canberra, Australia, last week, Eugene Kaspersky — the head of the anti-virus and cyber protection firm with the same name — was tipped off about the damage by a colleague who works at the Russian plant.