The attackers took great pains to learn each bank’s particular system, while they set up fake accounts at banks in the United States and China that could serve as the destination for transfers. Two people briefed on the investigation said that the accounts were set up at J.P. Morgan Chase and the Agricultural Bank of China. Neither bank returned requests for comment.
Kaspersky Lab was founded in 1997 and has become one of Russia’s most recognized high-tech exports, but its market share in the United States has been hampered by its origins. Its founder, Eugene Kaspersky, studied cryptography at a high school that was co-sponsored by the K.G.B. and Russia’s Defense Ministry, and he worked for the Russian military before starting his firm.
When the time came to cash in on their activities — a period investigators say ranged from two to four months — the criminals pursued multiple routes. In some cases, they used online banking systems to transfer money to their accounts. In other cases, they ordered the banks’ A.T.M.s to dispense cash to terminals where one of their associates would be waiting.
But the largest sums were stolen by hacking into a bank’s accounting systems and briefly manipulating account balances. Using the access gained by impersonating the banking officers, the criminals first would inflate a balance — for example, an account with $1,000 would be altered to show $10,000. Then $9,000 would be transferred outside the bank. The actual account holder would not suspect a problem, and it would take the bank some time to figure out what had happened.
“We found that many banks only check the accounts every 10 hours or so,” Mr. Golovanov of Kaspersky Lab said. “So in the interim, you could change the numbers and transfer the money.”
The hackers’ success rate was impressive. One Kaspersky client lost $7.3 million through A.T.M. withdrawals alone, the firm says in its report. Another lost $10 million from the exploitation of its accounting system. In some cases, transfers were run through the system operated by the Society for Worldwide Interbank Financial Telecommunication, or Swift, which banks use to transfer funds across borders. It has long been a target for hackers — and long been monitored by intelligence agencies.
Mr. Doggett likened most cyberthefts to “Bonnie and Clyde” operations, in which attackers break in, take whatever they can grab, and run. In this case, Mr. Doggett said, the heist was “much more ‘Ocean’s Eleven.’ ”