According to government and cyber-industry experts testifying at a hearing on Capitol Hill on Wednesday, the Windows OS worm Stuxnet - which was discovered this past July - is an incredibly large, complex threat with capabilities that have never been seen before.

While testifying at a hearing held by the Senate Committee on Homeland and Security Affairs, Dean Turner, Symantec's director of Global Intelligence Network for Symantec Security Response, said that Stuxnet was "one of the most complex threats we have analyzed to date."

Noting that highly-complex computer attacks using Stuxnet apparently pose a serious security threat to critical infrastructure round the world, the experts said that the worm particularly targets those systems that run the electric power grid, water treatment, and oil and gas pipelines.

Turner informed the lawmakers that there were as many as 44,000 unique Stuxnet infections worldwide, with 1,600 of them in the US; and almost 60 percent of the global infections were in Iran, where extremely complex computer attacks have probably been targeting the country's nuclear power plants.

Talking about the Stuxnet worm, Sean McGurk - who heads Department of Homeland Security's Cybersecurity Center - told the committee that the code can "automatically enter a system, steal the formula for the product you are manufacturing, alter the ingredients being mixed in your product, and indicate to the operator and your anti-virus software that everything is functioning as expected."