Nasdaq computers compromised by hackers

The Nasdaq situation has set off alarms within the government because of the exchange's critical role, which officials put right up with power companies and air-traffic-control operations, all part of the nation's basic infrastructure. Other infrastructure components have been compromised in the past, including a case in which hackers planted potentially disruptive software programs in the U.S. electrical grid, according to current and former national-security officials.

"So far, [the perpetrators] appear to have just been looking around," said one person involved in the Nasdaq matter. Another person familiar with the case said the incidents were, for a computer network, the equivalent of someone sneaking into a house and walking around but—apparently, so far—not taking or tampering with anything.