Library of Congress email systems hacked earlier this year by 'foreign adversary'

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.

The hack was described to Fox News as "classic, sophisticated foreign adversary espionage."

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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.