China proves to be an aggressive foe in cyberspace

Wolf said that the offices of 17 House members have been targeted. "Not a week doesn't go by when there's not a Chinese attack on our government," he said.

One day last spring, Capitol Hill security officials removed two computers from a congressional office that deals with foreign affairs. "There's a bug in your computer," one agent told an astonished staffer. "From China."

Director of National Intelligence Dennis C. Blair said in February that Russia and China were able to "to target and disrupt elements of the U.S. information infrastructure" and that China was "very aggressive" in cyberspace.

Another problem is China's ability to leave behind malicious sleeper code that can one day be activated to alter or destroy information. In April, then-National Counterintelligence Executive Joel F. Brenner reported that the Chinese had penetrated "certain of our electricity grids" with malicious code and that "our networks are being mapped"

One challenge in countering the threat, experts say, is that the Chinese often contract out such work to experts in industry and academia and possibly even to freelance hackers, allowing officials to argue that while an attack might have originated from an Internet service provider in China, no one could prove it came from the government.

The Chinese People's Liberation Army has publicly embraced such outsourcing. In 2002, the PLA created information warfare units, comprising operators and analysts from the commercial sector and academia, according to a new report by defense contractor Northrop Grumman for the U.S.-China Economic and Security Review Commission, a congressionally chartered body.

A year later, China's Academy of Military Sciences published an account of a trial project in the Guangzhou Military Region to establish information-warfare militia units using local telecommunications companies as a source of talent, funding and technology. Subsequently, the academy directed the PLA to make creation of such units a priority.

"Information warfare is not just a theology," said Ming Zhou, a China specialist with VeriSign iDefense, a security intelligence firm. "They can integrate it into nation-state interests."

Some U.S. cyber policy experts such as James A. Lewis, a senior fellow with the Center for Strategic and International Studies, acknowledge that the problem cannot be solved without international engagement. At the same time, Lewis said, "I'm not going to get upset about China spying on us, because we spy on them."

"The only thing I'm going to get upset about," he said, "is if we don't do better than them."