Hackers or foreign governments may have had access to White House Chief of Staff John Kelly's personal phone as far back as December.
That's according to a report from Politico, citing three US government officials.
A spokesman for the White House was not immediately available for comment.
The potential breach highlights the fact that anyone can be susceptible to a hack, an issue made evident by the widespread attacks ranging from the WannaCry software exploit to Americans having their data exposed in the Equifax hack.
The White House told Politico that Kelly had not used the phone since joining the administration, and relied on a government-issued handset for official communications. One of the officials told the political news site that Kelly was using a different personal phone.