Updated

The FBI and other federal agencies are investigating a coordinated computer hack targeting JPMorgan Chase and at least four other American banks, according to multiple published reports late Wednesday.

Bloomberg News, citing a U.S. official and a person briefed by law enforcement, reported that the attackers stole personal data that can be used to empty bank accounts. A third person told Bloomberg that employee data was also targeted and that the scale of the theft indicated the potential for serious fraud.

Bloomberg reported that the FBI was looking at whether Russian hackers were involved as a way of retaliating for economic sanctions placed on Moscow due to its involvement in the ongoing conflict with Ukraine. The site's report cited security experts saying that the attack appeared "far beyond the capability of ordinary criminal hackers."

However, an analyst quoted by The Washington Post said that any Russian cyber-retaliation was more likely to involve disruption of networks, not data theft. Bloomberg reported that that investigators had not ruled out Russian or Eastern European cybercriminals.

FBI Supervisory Special Agent Joshua Campbell told the Post that the FBI was working with the Secret Service "to determine the scope of recently reported cyber attacks against several American financial institutions." Bloomberg reported that the National Security Agency was also helping in the probe.

Security breaches at large banks like JPMorgan Chase are rare due to the multiple layers of security around their networks. Spokeswoman Patricia Wexler emailed a statement to the Associated Press and other news outlets saying in part that “companies of our size unfortunately experience cyber attacks nearly every day. We have multiple, layers of defense to counteract any threats and constantly monitor fraud levels."

JPMorgan is the largest U.S. bank by assets.

The Associated Press contributed to this report. 

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