The U.S. agency charged with ensuring that voting machines meet security standards was itself penetrated by a hacker after the November elections, according to a security firm working with law enforcement on the matter.

The security firm, Recorded Future, was monitoring underground electronic markets where hackers buy and sell wares and discovered someone offering log-on credentials for access to computers at the U.S. Election Assistance Commission, company executives said.

Posing as a potential buyer, the researchers engaged in a conversation with the hacker, said Levi Gundert, vice president of intelligence at the company, and Andrei Barysevich, director of advanced collection.