By now, you should all be familiar with the Stuxnet computer virus detailed last night on 60 Minutes. The worm, first discovered in mid 2010 after successfully targeting and disrupting uranium enrichment facilities in Iran, was almost certainly developed with US and Israeli participation. It's also thought to be the most sophisticated cyber weapon ever created having managed to elude the detection of Iranian plant operators even as it spun hundreds of centrifuges beyond their breaking points.
Now that the Stuxnet source code is available for download (it took a CBS producer about a week to find it on "hacking sites"), it can be studied and possibly repurposed and repackaged by any motivated individual or organization to attack the programmable logic controllers crucial to the operation of national infrastructure services like traffic systems, power grids, or water treatment facilities — any industrial system that relies upon PLCs. A Pandora's Box, if you will, that could be turned against the creators of Stuxnet for mischief or cyberwarfare.