Reporters covering national security and economic policy were among the employees affected by the breach.

The Post discovered the “possible targeted” hack of its email system last Thursday, prompting the newspaper to reset login credentials for all its employees on Friday, Washington Post Executive Editor Matt Murray said in a memo Sunday to employees.

The Washington Post and Microsoft have not yet commented regarding the incident. This is not the first time The Washington Post has found itself in the crosshairs of cyber adversaries; the newspaper has faced a series of breaches dating back to 2011, with some past attacks attributed to Chinese groups.