Members of President Donald Trump’s National Security Council, including White House national security adviser Michael Waltz, have conducted government business over personal Gmail accounts, according to documents reviewed by The Washington Post and interviews with three U.S. officials.

The use of Gmail, a far less secure method of communication than the encrypted messaging app Signal, is the latest example of questionable data security practices by top national security officials already under fire for the mistaken inclusion of a journalist in a group chat about high-level planning for military operations in Yemen.