A computer hacker penetrated the personal information of about 26,000 D.C.-area Department of Agriculture employees and contractors because the department told its security agency to shut down its anti-hacker system, sources said.

It’s not clear how much damage has been wrought by the June 5 breach. AT&T — the company contracted to protect the department’s computer system from hackers — had no comment. But sources said it was given permission to shut the security system down.