Last summer’s vast and hugely symbolic plundering of customer accounts at US banks JPMorgan Chase & Co might not have been the work of Russian hacktivists protesting about sanctions, the FBI has told US journalists at a round table briefing.

Exactly what journalists were told in the meeting is open to some interpretation, with some reports writing off Russian state involvement while others stating that officials were simply not sure about the motivations of the attackers.

The tone might be ambiguous but the significance of what came to light in an SEC filing by JPMorgan Chase on 2 October is not in doubt – sometime between June and July of this year a data breach compromised the name, address, phone number  and email address of 76 million consumers and seven million small business accounts.

At the time, bank officials appeared to pin the blame on Russian attackers retaliating for US sanctions on the country, something the US authorities now appear to ber downplaying.

“There’s no indication that [the attack was] as a result of the sanctions,” FBI Cyber Division assistant director Joseph M. Demarest was quoted as telling The Washington Post and others.

“There’s a blending,” Demarest added, referring to the connections professional criminality and freelance actions motivated by politics.

“They may be working as criminals by evening or dark of night and then during the day they’re working on behalf of some government.”

Adding to anxiety were subsequent reports that the attackers who picked out JPMorgan Chase had attacked up to 13 other US financial institutions. A breach at one bank might be expected from time to time but the possibility that it had happened at a dozen or more within a short period of time started to look like something more significant.

The attacks were taken seriously enough for President Obama, reportedly, to be regularly briefed on the investigation into their source.

The emergence of Russia as a serious foe in cyberspace parallels similar worries in the US about China since 2010, Iran from 2012 onwards and to a much smaller extent, Syria and North Korea.