Reports say hackers gained access to the networks of at least five banks, including JPMorgan Chase (JPM), and funneled off gigabytes of data.

The sophisticated cyberattack, as experts call it, included access to checking and savings account information, reported the New York Times. The Federal Bureau of Investigation has been investigating and security firms specializing in digital forensic studies have been tapped to study the intruded networks in recent weeks.

The reasons behind the attacks are unclear. Authorities have not confirmed the origin of the hackers or whether the events were motivated by financial or espionage reasons. Bloomberg News first reported the breaches and indicated that it was the work of Russian hackers, though that has not been confirmed officially.

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Russian hackers have previously assaulted foreign computer networks as retaliation, including a crippling attack on Estonia’s networks in 2007 after workers moved a Soviet-era war monument from the country’s capital.

Other politically-motivated hacking scandals included Iran’s denial of service, or DDoS, attacks on U.S. banks following Western economic sanctions and an anti-Islam video mocking the Prophet Muhammad. The DDoS attacks caused banking websites to drastically slow or intermittently collapse.

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The nature of the most recent banking intrusions doesn’t appear to be politically driven. Banking site services weren’t disrupted during the attacks, which appear to be intended to gather financial or intelligence information, people with knowledge of the investigation told the Times.

JPMorgan has not seen heightened levels of fraud as of yet, possibly a sign that the hackers may not have been after only financial information. Until security firms present conclusive evidence, officials cannot confirm the reason or source of the attacks.

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