One or more unknown people accessed White House chief of staff Susie Wiles’ personal cellphone and used her contacts file to reach out to other top officials and impersonate her, sources told CBS News Thursday.

Some of the recipients realized the messages were suspicious because the texts and calls came from an unknown number, sources said, and the impersonator or impersonators asked if the conversations could be continued in another platform, such as Telegram.

The suspicious messages hit in-boxes over an unknown period of time, sources said. 

Wiles explained to people that her phone had been hacked, sources told CBS News.  

The Wall Street Journal earlier Thursday reported on the incident and the federal probe launched in response.

“The White House takes the cybersecurity of all staff very seriously, and this matter continues to be investigated,” a White House spokesperson told CBS News when asked about the details of the situation. 

FBI Director Kash Patel said in a statement shared with CBS News: “The FBI takes all threats against the President, his staff, and our cybersecurity with the utmost seriousness; safeguarding our administration officials’ ability to securely communicate to accomplish the President’s mission is a top priority.”