A US Department of Defense watchdog has opened an investigation into its own Secretary of Defense, Pete Hegseth, over his use of instant-messaging app Signal to discuss government business.

In a Thursday memorandum, the dept’s acting Inspector General (IG) Steven Stebbins wrote [PDF] that a probe will be carried out in response to a letter [PDF] last month from the two ranking members of the Senate Armed Services Committee, Senators Roger Wicker (R-MS) and Jack Reed (D-RI).

The pair of lawmakers asked Trump-appointed Stebbins and his office to look into why Signal was being used by Hegseth, if classified information had been shared by the Defense Secretary using the encrypted chat app, and if Pentagon security guidelines had been broken.

Atlantic magazine editor-in-chief Jeffery Goldberg revealed Hegseth’s use of Signal after the journo was inadvertently added to a private group chat in which the Defense Secretary and other senior US officials discussed a forthcoming airstrike against Houthi rebels in Yemen. The chat detailed targets, the timing of the attack, the aircraft used, and other information one might assume would ordinarily be classified.

National Security Advisor Michael Waltz hosted the Signal group, and had accidentally added Goldberg. Members included US Vice President JD Vance, Hegseth, Secretary of State Marco Rubio, CIA Director John Ratcliffe, Director of National Intelligence Tulsi Gabbard, and Homeland Security Advisor Stephen Miller.

All have since insisted no rules requiring the preservation of government documents were broken; some of the messages were set to auto-delete. They also claimed the military plans were not classified.

The existence of the group was embarrassing given past Republican opposition to public officials using private communications services. It’s since been reported that Waltz routinely uses his personal Gmail account for government business, and has established up to 20 private government-related Signal groups.

“This chat was alleged to have included classified information pertaining to sensitive military actions in Yemen,” the two senators wrote. “If true, this reporting raises questions as to the use of unclassified networks to discuss sensitive and classified information, as well as the sharing of such information with those who do not have proper clearance and need to know.”

The IG will conduct his investigation in Washington DC and at US Central Command in Florida, and instructed Secretary Hegseth to assign two points of contact for him – one a government official, and the other a senior military officer – within the next five days.

“The objective of this evaluation is to determine the extent to which the Secretary of Defense and other DoD personnel complied with DoD policies and procedures for the use of a commercial messaging application for official business,” the watchdog’s letter reads.

“Additionally, we will review compliance with classification and records retention requirements. We may revise the objective as the evaluation proceeds.”

The wording of the letter is very formal, even a little intimidating, though President Trump has already indicated he’s not concerned with his team’s use of Signal. Stebbins was installed as acting IG after his predecessor and 16 other Inspectors General throughout the federal government were dismissed by the commander-in-chief on January 24. ®