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Thousands of confidential documents from the Washington, D.C. Metropolitan Police Department were leaked onto the dark web Thursday after a cyberattack from a "Russian-speaking ransomware syndicate," The Associated Press reports.

The leak includes "hundreds of police officer disciplinary files and intelligence reports," as well as "feeds from other agencies," like "the FBI and Secret Service," AP writes. It is, according to experts, "the worst known ransomware attack ever to hit a U.S. police department."

The so-called Babuk Group coordinated the leak after the D.C. police department "refused to meet" blackmail demands. The group reportedly asked for $4 million in ransom, but were "only offered $100,000." The department has not clarified whether or not it made the offer, per AP.

Last month, the ransomware gang revealed its cyberattack and threatened a massive leak. Some of the data they reportedly obtained includes "sensitive and embarrassing private details" from background checks, as well as documents detailing security operations at events like President Biden's inauguration.

The breach comes just one day after the Colonial Pipeline resumed operations following its own ransomware attack last week. Read more at The Associated Press.