A silent attack,but not so subtle

The malware was so skillfully designed that computer security specialists who have examined it were almost certain it had been created by a government and is a prime example of clandestine digital warfare. Stuxnet is the first virus to go after industrial systems.

Stuxnet was splattered on thousands of computer systems around the world,rather than on what appears to have been its intended target,Iranian equipment. Global alarm over the deadly computer worm has come many months after the programme was suspected of stealthily entering an Iranian nuclear enrichment plant.

Much speculation about the target has focused on the Iran nuclear plant at Natanz. In mid-July the Wikileaks Web site reported that it had learned of a serious nuclear accident at the plant. But international nuclear inspectors say no evidence of one exists.

The head of the Bushehr nuclear plant in Iran said Sunday that the worm had affected only the personal computers of staff members,Reuters reported. Western nations say they do not believe Bushehr is being used to develop nuclear weapons. Citing the state-run newspaper Iran Daily,Reuters reported that Irans telecommunications minister,Reza Taghipour,said the worm had not penetrated or caused serious damage to government systems.

Siemens has said that the worm was found in only 15 plants around the world using its equipment and that no factorys operations were affected. But the programme is continuing to spread through computer systems around the world through the Internet.

Stuxnet has laid bare significant vulnerabilities in industrial control systems.

Proliferation is a real problem,and no country is prepared to deal with it, said Melissa Hathaway,a former United States national cybersecurity coordinator. We have about 90 days to fix this before some hacker begins using it.

The ability of Stuxnet to infiltrate these systems will require a complete reassessment of security systems and processes,starting with federal technology standards and nuclear regulations,said Joe Weiss,a specialist in the security of industrial control systems who is managing partner at Applied Control Solutions in Cupertino,California.

One big question is why its creators let the software spread widely,giving up many of its secrets in the process.

One possibility is that they simply did not care. Their government may have been so eager to stop the Iranian nuclear programme that the urgency of the attack trumped the tradecraft techniques that traditionally do not leave fingerprints,digital or otherwise.

It is likely that there have been many other attacks of similar or even greater sophistication by intelligence agencies from many countries in the past. What sets this one apart is that it became highly visible.

Security specialists contrast Stuxnet with an intrusion discovered in the Greek cellphone network in March 2005. A two-year investigation by the Greek government found an extremely sophisticated Trojan horse programme that had been hidden by someone who was able to modify and then insert 29 secret programmes into each of four telephone switching computers. The level of skill needed to pull off the operation and the targets strongly indicated a government.

Another case is of the 2007 Israeli Air Force attack on what was suspected of being a Syrian nuclear reactor under construction. Accounts of the event initially indicated that sophisticated jamming technology had been used to blind the radar so Israeli aircraft went unnoticed. Last December,however,a report in an American technical publication,IEEE Spectrum,raised the possibility that the Israelis had used a built-in kill switch to shut down the radar.

A former member of the United States intelligence community said the attack had been the work of Israels equivalent of Americas National Security Agency,known as Unit 8200. But if the attack was based on a worm or a virus,there was never a smoking gun like Stuxnet.