FBI officials are investigating a recently disclosed cyberattack on Yahoo that occurred in August 2013 and may have impacted more than 1 billion users’ accounts, White House press secretary Josh Earnest confirmed Thursday.

Earnest said he could not address the scope of the material that may have been compromised in the hack because the matter is being investigated by the FBI. Agency officials are unlikely to make the entirety of their findings public since the investigation involves individuals’ personal and private information, he added.