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.
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"The Library of Congress recently discovered a cyber breach of the Library's information technology environment whereby an adversary accessed email communications during the timeframe of January to September 2024 between Library staff and congressional offices," Library of Congress spokesman Bill Ryan told Fox News.
"The Library has mitigated the vulnerability that the adversary used to access these emails and has taken measures to prevent such incidents in the future. The Library has referred the matter to law enforcement and is also conducting its own analysis of the breach."
The hack was described to Fox News as "classic, sophisticated foreign adversary espionage."
This means that the foreign actor conducting the hack was likely trying to get a sense of what types of questions lawmakers and aides ask the Library of Congress about legislation and the answers they receive.
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If successful, such espionage could shed light on the thinking of lawmakers about certain subjects.
Fox is told that it took some prompting by senior Congressional officials to share what went down at the Library of Congress. However, the hack is not believed to have spread to other Congressional systems - like the House and Senate.
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In addition, it is believed that the hackers went after the Library of Congress due to it being a "softer target" compared to the rest of Congress and lacks the more sophisticated systems which the rest of Congress uses to guard against cyber spying.
Fox News Digital reached out to the FBI, but it declined to comment.
Stepheny Price is writer for Fox News Digital and Fox Business. Story tips and ideas can be sent to stepheny.price@fox.com