WASHINGTON, Aug 25: US Defence Department websites are probed hundreds of times a day by hackers, but so far no classified site is known to have been penetrated by hackers, a spokesman said on Thursday.

The spokesman would not comment directly on a Washington Post report that said Chinese websites are being heavily used to break into unclassified US government computer networks.

“When it comes to Defence Department networks, ... we have a very aggressive effort to defend our networks,” said the spokesman, Bryan Whitman.

“We get probed hundreds of times a day, but most importantly, there have been no reports to date that suggest any of our classified networks have been penetrated.”

The Defence Department has some 12,000 local area networks with 3.5 million individual computers, he said.

All available tools are being used to blunt computer network attacks and identify their source, he said.

“But all networks have vulnerabilities,” he noted, “and the challenge that we have is to stay one step ahead of our adversaries.” Among the computer networks affected were those of the Departments of Defence, State, Energy and Homeland Security, the Post said.

Although classified systems have not been compromised, US officials are concerned that information pulled from various sources could yield useful intelligence to an adversary, the Post said.

“The scope of this thing is surprisingly big” and stretches back as far as two or three years, said one official.

Another official said the Federal Bureau of Investigation has opened an inquiry into the incidents, which have been codenamed Titan Rain. The daily said the FBI declined to comment on the matter. —AFP