www.politico.com
Katherine Tully-McManus
11/10/2025, 2:01pm ET

Library of Congress employees were informed to take caution when emailing the office of the congressional scorekeeper.
A cybersecurity breach discovered last week affecting the Congressional Budget Office is now considered “ongoing,” threatening both incoming and outgoing correspondence around Congress’ nonpartisan scorekeeper.

Employees at the Library of Congress were warned in a Monday email, obtained by POLITICO, that the CBO cybersecurity incident is “affecting its email communications” and that library staff should take a range of measures to protect themselves.

Library of Congress workers also were told to restrict their communication with the nonpartisan agency tasked with providing economic and budgetary information to lawmakers.

“Do NOT click on any links in emails from CBO. Do NOT share sensitive information with CBO colleagues over email, Microsoft Teams, or Zoom at this time,” the email reads.

“Maintain a high level of vigilance and verify the legitimacy of CBO communications by confirming with the sender via telephone that they sent the message,” the note continues.

Congressional staff are in regular communication with CBO regarding scores of legislation and cost estimates the agency prepares for bills in both the House and Senate.

There was no immediate information Monday about the broader implications that a legislative branch office was continuing to experience cybersecurity vulnerabilities.

A CBO spokesperson said last week that officials had taken “immediate action to contain” the breach as officials investigate the incident.

When asked for comment Monday about ongoing issues, the CBO spokesperson referred to the prior statement.

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