CBS News reports that the National Security Agency (NSA), an arm of the Pentagon, had “sent out an operational security special bulletin to its employees in February 2025 warning them of vulnerabilities in using the encrypted messaging application Signal.”

The NSA operates under the authority of the Director of National Intelligence, Tulsi Gabbard.

The Pentagon also sent out a memo warning of Signal’s vulnerabilities and use by Russian hackers, just days after that group chat.

“Several days after top national security officials accidentally included a reporter in a Signal chat about bombing the Houthi sites in Yemen, a Pentagon-wide advisory warned against using the messaging app, even for unclassified information,” NPR reported Tuesday.

“Russian professional hacking groups are employing the ‘linked devices’ features to spy on encrypted conversations,” the Pentagon’s memo warned.

It also notes that Google has identified Russian hacking groups who are “targeting Signal Messenger to spy on persons of interest.”

The Pentagon memo reminded users that “third-party messaging apps (e.g. Signal) are permitted by policy for unclassified accountability/recall exercises but are not approved to process or store non-public unclassified information.”

NPR’s Quil Lawrence noted that “NPR has seen DoD memo as far back as 2023 prohibiting mobile apps for discussing even much less sensitive info like ‘controlled unclassified information.'”

Last month, a Google Threat Intelligence memo warned of the use of apps like Signal by “military personnel, politicians, journalists, activists, and other at-risk communities.”

Critics argue that the use of Signal for “war plans” was against policy. During Tuesday’s Senate Intelligence Committee hearing CIA Director John Ratcliffe had insisted Signal was approved for use.

National security experts, including at least one former Trump administration official, have been highly critical of the use of the app by the 18-members in a chat.

President Trump’s Ukraine and Middle East envoy Steve Witkoff “was in Moscow, where he met with Russian President Vladimir Putin, when he was included in a group chat with more than a dozen other top administration officials — and inadvertently, one journalist — on the messaging app Signal,” CBS News reported on Tuesday. “Russia has repeatedly tried to compromise Signal, a popular commercial messaging platform that many were shocked to learn senior Trump administration officials had used to discuss sensitive military planning.”

Trump’s Director of National Intelligence, Tulsi Gabbard, acknowledged on Tuesday during a Senate Intelligence Committee hearing that she was overseas during the Signal chat. The Associated Press reported the DNI “wouldn’t say whether she was using her personal or government-issued phone because the matter is under review by the White House National Security Council.”

The Wall Street Journal’s chief foreign-affairs correspondent Yaroslav Trofimov appears to be one of the first to note that Witkoff had been in Moscow during the time the chat had been organized. He notes: “The Signal app itself has high encryption. But if your phone is inside Russia, and especially if your WiFi and Bluetooth are not disabled, Russia can see what is inside your phone pretty easily.”

On Tuesday morning, Rep. Dan Goldman (D-NY) noted: “Not a single person out of 18 of the very most senior officials in this Admin — including the Director of National Intelligence and the CIA Director — voiced any concern with highly classified military plans circulated on Signal. You also can be sure this is not the only time.”

The Atlantic’s Dr. Norman Ornstein, a political scientist and scholar, responded to Rep. Goldman, writing: “Putin is giddy. He has compromised the phones of every top national security official in the Trump administration. No doubt has enough juicy information from what is likely to be multiple Signal chats to deeply damage American security. And possibly to blackmail some of them.”