The Chinese government has always opposed any Internet-wrecking crime, including hacking, and cracked down on it according to the law," Chinese Foreign Ministry spokeswoman Jiang Yu told reporters.
"Officially, the United States has not accused Beijing of cracking into the military e-mail system that serves Defense Secretary Robert Gates and hundreds of other department employees.
But, behind the scenes, a senior Bush administration official told CNN that China is the No. 1 suspect in the June hacking incident. On Monday, the Financial Times of London also reported that Washington believed China was responsible.
"Some people are making wild accusations against China and wantonly saying the Chinese military attacked the Pentagon's computer network," Jiang said. "These are totally groundless and also reflect a Cold War mentality."
She called hacking an international problem and said that China has also been attacked.
"China would like to work with other countries to take measures to crack down on Web crime," according to Jiang.
In Australia ahead of the APEC summit, reporters asked President Bush on Wednesday if he would bring up the issue of hackers with Chinese President Hu Jintao when the two leaders meet Thursday.
"I'm very aware that a lot of our systems are vulnerable to cyber attack from a variety of places," Bush said at a joint news conference with Australian Prime Minister John Howard.
"In terms of whether or not I'll bring this up to countries that we suspect may -- from which there may have been an attack, I may."
The cyber attack led the Pentagon to shut down its unclassified e-mail for nearly three weeks. U.S. government sources said the unclassified e-mail system is not connected to other e-mail networks that contain sensitive military secrets.
Pentagon officials said none of their operations were disrupted.
At the time of the attack, Gates never mentioned China.
"The reality is that the Defense Department is constantly under attack," he said. "Elements of the OSD [Office of the Secretary of Defense] unclassified e-mail system were taken off-line ... due to a detected penetration."
The Pentagon does suspect the Chinese People's Liberation Army (PLA) of operating secret cells of computer hackers, although not officially pointing a finger at Beijing in this instance.
In its annual report on the Chinese military earlier this year, the Defense Department confirmed the likely existence of such units: "The PLA has established information warfare units to develop viruses to attack enemy computer systems and networks."
On Wednesday, The Guardian newspaper in London reported that Chinese hackers launched online assaults against the network at Britain's Parliament and the Foreign Office, according to the Associated Press.
AP further reports that on the eve of German Chancellor Angela Merkel's visit to Beijing last week, the weekly Der Spiegel said computers at the Chancellery and three ministries had been infected with so-called Trojans, or spy programs.