The hackers behind the JP Morgan attack targeted nine other financial groups, according to sources close to the investigation.
It is unknown which other banks were hit and to what extent they were penetrated, but they are thought to be working from Russia, and may have connections to the Russian government.
Speaking to the New York Times, a senior official said: "It could be in retaliation for the sanctions [placed on Russia]…but it could be mixed motives — to steal if they can, or to sell whatever information they could glean."
The attack on JP Morgan was first discovered in July, but the extent of it remained unknown for several months before it was revealed to have affected 83 million customers, 7 million of which were business account holders.
Though no financial information was taken from the accounts, contact information such as names, addresses and telephone numbers was stolen, prompting speculation that victims may be profiled in the future.
Barry Scott, CTO at identity management firm Centrify, said: "Loss of data such as names, e-mail addresses, home addresses and phone numbers are all part of the jigsaw that make up a person’s digital presence, and can form a good basis for further targeted attacks on that individual and the other services they use."
Yet customers of the bank rallied in the wake of the attack, with JP Morgan spokeswoman Trish Wexler saying that people were not leaving the bank because of the breach.
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The speculation that Russians may be targeting US banks for political reasons comes as Federal Bureau of Investigation director James Comey told the television show 60 minutes that Chinese hackers were costing the country billions.
"There are two kinds of big companies in the United States," he said. "There are those who’ve been hacked by the Chinese, and those who don’t know they’ve been hacked by the Chinese."
