The Chinese military hacked into a Pentagon computer network in June in the
most successful cyber attack on the US defence department, say American
­officials.

The Pentagon acknowledged shutting down part of a computer system serving the
office of Robert Gates, defence secretary, but declined to say who it believed
was behind the attack.

Current and former officials have told the Financial Times an internal
investigation has revealed that the
incursion came from the People’s Liberation Army.

One senior US official said the Pentagon had pinpointed the exact origins of
the attack. Another person familiar with the event said there was a “very high
level of confidence…trending towards total certainty” that the PLA was
responsible. The defence ministry in Beijing declined to comment on Monday.

Angela Merkel, Germany’s chancellor, raised reports of Chinese infiltration
of German government computers with Wen Jiabao, China’s premier, in a visit to
Beijing, after which the Chinese foreign ministry said the government opposed
and forbade “any criminal acts undermining computer systems, including
hacking”.

“We have explicit laws and regulations in this regard,” said Jiang Yu, from
the ministry. “Hacking is a global issue and China is frequently a victim.”

George W. Bush, US president, is due to meet Hu Jintao, China’s president, on
Thursday in Australia prior to the Apec summit.

The PLA regularly probes US military networks – and the Pentagon is widely
assumed to scan Chinese networks – but US officials said the penetration in June
raised concerns to a new level because of fears that China had shown it could
disrupt  systems at critical times.

“The PLA has demonstrated the ability to conduct attacks that disable our
system…and the ability in a conflict situation to re-enter and disrupt on a
very large scale,” said a former official, who said the PLA had
penetrated the networks of US defence companies and think-tanks.

Hackers from numerous locations in China spent several months probing the
Pentagon system before overcoming its defences, according to people familiar
with the matter.

The Pentagon took down the network for more than a week while the attacks
continued, and is to conduct a comprehensive diagnosis. “These are multiple
wake-up calls stirring us to levels of more aggressive vigilance,” said Richard
Lawless, the Pentagon’s top Asia official at the time of the attacks.

The Pentagon is still investigating how much data was downloaded, but one
person with knowledge of the attack said most of the information was probably
“unclassified”. He said the event had forced officials to reconsider the kind of
information they send over unsecured e-mail systems.

John Hamre, a Clinton-era deputy defence secretary involved with cyber
security, said that while he had no knowledge of the June attack, criminal
groups sometimes masked cyber attacks to make it appear they came from
government computers in a particular country.

The National Security Council said the White House had created a team of
experts to consider whether the administration needed to restrict the use of
BlackBerries because of concerns about cyber espionage.

Additional reporting by Richard McGregor in Beijing

To contact the reporter email demetri.sevastopulo@ft.com