Computer experts say Stuxnet is the first known case of cyber sabotage. Discovered just a few months ago, it's a virus that infects not just computer programs but also the machines they operate. It's so sophisticated that it's likely the work of a nation-state targeting Iran's nuclear program. But it's also spread to a number of other countries. Is Stuxnet a cyber-warfare weapon that went wrong? Who launched it? Nobody knows, but the Internet could be used to wreak havoc in the real world. What are the challenges for national security? Will it mean compromising the freedom and privacy now taken for granted in the virtual world?