A least five banks were struck by hackers this month, according to a U.S. official.
J.P. Morgan, one of the involved banks whose name was released, appeared to be attacked through an employee's personal computer, a source involved with the investigation tells The Wall Street Journal. This led the intruder deeper into the bank's inner systems.
Some investigators believe that the attacks, appearing to derive from malware (a malicious computer code), came from a Russian or Eastern European link, reports WSJ, though it's too early to confirm who is behind the breach.
Although J.P. Morgan was reportedly involved, the company has maintained officials did not see any fraudulent or unusual behavior in its systems .
"Companies of our size unfortunately experience cyber-attacks nearly every day," Patricia Wexler, a JPMorgan spokeswoman, tells Business Week.
It has not yet been confirmed whether the stolen information resulted in a financial loss for customers.
