On 18 March, the Pentagon sent a department-wide “OPSEC special bulletin” warning employees against using Signal, citing a technical vulnerability that could be exploited by Russian hacking groups to spy on encrypted communications and potentially target “persons of interest,” according to NPR.
The warning was reported a day after the Atlantic described how senior Trump administration national security officials—including Vice-President JD Vance and Defense Secretary Pete Hegseth—used a Signal group chat for discussion of planned military strikes in Yemen and inadvertently added the Atlantic editor-in-chief, Jeffrey Goldberg.
The Pentagon memo stated that third-party messaging apps like Signal may be used for unclassified information but may not be used to transmit “non-public” unclassified information.
Goldberg reported receiving details about a forthcoming series of airstrikes on 15 March, hours before the strikes occurred. Trump administration officials publicly downplayed the sensitivity of the exposed information, and Trump characterized the incident as a “glitch.”