LONDON, Aug. 17 -- When the text appeared on his screen, it looked like a message from the most powerful aide in the White House. For a brief window, UK Prime Minister Andy Burnham was exchanging messages with someone he believed to be Susie Wiles, Donald Trump's chief of staff and among the most closely guarded officials in Washington.

He was not.

The incident, first reported by the Sunday Times and confirmed Sunday by Anadolu Agency, adds the sitting British prime minister to a growing list of targets caught in a sophisticated impersonation campaign tied to the May hack of Wiles' personal phone. Attackers who breached her device did not just steal data. They walked away with her contact list, a directory of world leaders, senior diplo...