Secretary of Defense Pete Hegseth should stop using the Signal messaging app at this point.

The Washington Post reports that the former Fox News host had Signal installed on his office computer at the Pentagon, a major security risk and further evidence that Hegseth used the messaging tool frequently for government business. According to the Post, the desktop app mirrored Hegseth’s phone and helped the secretary overcome the lack of cell phone service within the Pentagon.

Cell phones and other personal electronic devices are not permitted within classified spaces, and installing Signal on his desktop computer allowed Hegseth to get around that prohibition. At least one of Hegseth’s top aides, his chief of staff Joe Kasper, also expressed interest in using Signal on Department of Defense computers, but it’s not clear how widespread the app is among Pentagon employees.