The most pernicious computer virus ever known wasn't out to steal your money, identity, or passwords. So what was the intricate Stuxnet virus after? Its target appears to have been the centrifuges in a top secret Iranian nuclear facility. Stuxnet showed, for the first time, that a cyber attack could cause significant physical damage to a facility. Does this mean that future malware, modeled on Stuxnet, could target other critical infrastructure -- such as nuclear power plants or water systems? What kind of risk do we face in this country? Steve Kroft reports.