Morgan Stanley suffered a "very sensitive" break-in by the Chinese computer hackers who attacked Google last year, according to leaked emails from an internet security firm working for the investment bank.
The emails, which were sent by California-based HB Gary Federal, detail how Morgan Stanley was "hit hard" by a six-month strong attack on its network in June 2009 – within weeks of the attack on Google by Chinese hackers.
George Kurtz, chief technology officer for security firm McAfee which investigated the so-called "Operation Aurora" attacks, described it as the "largest and most sophisticated cyberattack we have seen in years".
An email sent by Phil Wallisch, a senior security engineer at HB Gary Federal, which provided internet security for Morgan Stanley, said: "They [Morgan Stanley] were hit hard by the real Aurora attacks (not the crap in the news).
"They have given me access to a very sensitive report on their Aurora experience," Wallisch said in an email to a colleague in May last year. "I will honor their wishes about not sharing the info with anyone, but the good news is that I have some great ideas for our final reports."
The HB Gary Federal emails were made public in the wake of an attack by online collective Anonymous. The emails did not reveal what information may have been stolen from Morgan Stanley.
Morgan Stanley declined on Monday to comment specifically on the Operation Aurora attack. A spokeswoman said: "Morgan Stanley invests significantly in IT security and manages a robust programme to deal with malware and attempted computer compromises."
A senior member of China's communist politburo organised the hack into Google, according to leaked classified information sent by US diplomats in China to Hillary Clinton's state department, revealed by WikiLeaks.
Google made public the "highly sophisticated and targeted attack" last January, shortly before the hackers shut down their operation. The attack, which involved "more than 20 other US companies", was partly aimed at the Gmail accounts of "Chinese human rights activists".
Classified diplomatic cables sent by the US embassy in Beijing, and released by WikiLeaks in December, alleged that a leading Chinese politician had "coordinated" the assault on Google, which the Americans claimed was "100% political in nature".
The attack caused Google to abandon mainland China and sparked a global diplomatic row about internet censorship.
Hillary Clinton, the US secretary of state, renewed her calls for China and other countries to adopt common standards for internet use, which includes removing barriers to access.
• Booby-trapped adverts hit visitors to the London Stock Exchange (LSE) website on Monday. The ads, which the LSE said were provided by a third party, caused some users' computers to crash – with one victim claiming his machine became unusable after landing on the site. The LSE site has been involuntarily hosting computer viruses on around 363 pages in the last 90 days, according to an analysis by Google.