The Library of Congress email systems suffered a substantial hack earlier this year by a "foreign adversary," Fox News can confirm.
It is unclear if the hack compromised accounts of those who work directly for the House and Senate.
However, Fox News is told that U.S. Capitol Police has referred the matter to the FBI, and it is investigating the scope of the hack.
Fox is told the Library of Congress notified impacted congressional personnel in the House and Senate, which included both Republican and Democratic offices.