SC Magazine reported yesterday that the camera-loving celebrity's Sidekick has been hacked into and that dozens of her celebrity friends' private mobile numbers were available online.
In a statement, Bryan Zidar, senior manager of media relations at T-Mobile US, said that an investigation was already underway.
"T-Mobile's computer forensics and security team is actively investigating to determine how Ms. Hilton's information was obtained. This includes the possibility that someone had access to one of Ms. Hilton's devices and/or knew her account password," Zidar said.
He then offered tips to other Sidekick users including use of complex passwords and regular changing of passwords.
Some members of the press were able to contact the celebrities listed yesterday. The New York Daily Times spoke to reality TV personality Victoria Gotti who claimed to have received hundreds of calls.
"This went on all night. Finally, at 5.30am, I took them off the hook. This morning, I put them back on and they started ringing immediately. It's driving me insane."
Paris Hilton is often at the centre of online activity. Yesterday anti-virus firm Sophos warned that two different worms, referencing Hilton and promising illicit images, were doing the internet rounds. Sober-K and Ahker-C masquerade as x-rated videos but actually open backdoors for other viruses and spyware.
"It's an old trick but sadly it still often works," said Graham Cluley, senior technology consultant at Sophos.