Russians hacked J.P. Morgan Chase and at least one other bank in mid-August immediately after the U.S. levied new sanctions on Moscow, according to an FBI probe. The attack resulted in the theft of gigabytes' worth of sensitive data and may be linked to similar recent infiltrations of European banks. People familiar with the case say the FBI suspects the attack was retaliation for the sanctions. Experts say the hackers' ability to move through sophisticated security suggests these were not average criminals—but the hackers left enough of a trail to also suggest the Russian government wasn't involved. The news comes as Russia pushes an invasion of Ukraine. “The Russians typically keep open the options to do something more, and the question now is what would trigger that and what would our response be,” said James Lewis, director of the Strategic Technologies program at the Center for Strategic and International Studies.