The 3.4 million figure “is certainly a large number,” a senior FBI official said in a press briefing Friday on the annual ODNI report on FBI surveillance. “I am not going to pretend that it isn’t.”

More than half of the reported searches—nearly two million—were related to an investigation into a national-security threat involving attempts by alleged Russian hackers to break into critical infrastructure in the U.S. Those searches included efforts to identify and protect potential victims of the alleged Russian campaign, senior U.S. officials said.

Officials declined to give more details on the alleged Russian threat, including whether it was linked to the Russian government or a criminal hacking group. Russia has historically denied accusations of hacking the U.S. or other nations.

The number of searches of American data doesn’t correspond to the number of Americans who may have had their personal information examined.