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The U.S. Congressional Budget Office has confirmed it was hacked.

Caitlin Emma, a spokesperson for CBO, told Read on Friday that the agency is investigating the breach and “has identified the security incident, has taken immediate action to contain it, and has implemented additional monitoring and new security controls to further protect the agency’s systems going forward.”

CBO is a nonpartisan agency that provides economic analysis and cost estimates to lawmakers during the federal budget process, including after legislative bills get approved at the committee level in the House and Senate.

On Thursday, The Washington Post, which first revealed the breach, reported that unspecified foreign hackers were behind the intrusion. According to the Post, CBO officials are worried that the hackers accessed internal emails and chat logs, as well as communications between lawmakers’ offices and CBO researchers.

Reuters reported that the Senate Sergeant at Arms office, the Senate’s law enforcement agency, notified congressional offices of a breach, warning them that emails between CBO and the offices could have been compromised and used to craft and send phishing attacks.

It’s unclear how the hackers gained access to the CBO’s network. But soon after news of the breach became public, security researcher Kevin Beaumont wrote on Bluesky that he suspected hackers may have exploited the CBO’s outdated Cisco firewall to break into the agency’s network.

Last month, Beaumont noted that CBO had a Cisco ASA firewall on its network that was last patched in 2024. At the time of his posting, the CBO’s firewall was allegedly vulnerable to a series of newly discovered security bugs, which were being exploited by suspected Chinese government-backed hackers.

Beaumont said the CBO’s firewall had not been patched by the time the federal government shutdown took effect on October 1.

On Thursday, Beaumont said that the firewall is now offline.

The CBO’s spokesperson declined to comment when asked about Beaumont’s findings. Spokespeople for Cisco did not immediately respond to a request for comment.