T-Mobile commented on their security. Apparently someone might have knew her account password and gain access to her data. Maybe her PC is hacked?

T-Mobile is investigating the reported disclosure of Paris Hilton's information.

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.

Given the sensitivity of the situation, and to protect our customers' information, we are not able to provide specific details of the investigation at this point.

To know more about her shared private photos

via www.engadget.com