
SpoofCard.com, which provides calling cards with which the caller can specify any outgoing caller ID number, stated that it has cancelled 50 accounts that were using the service to break into voicemail accounts.
The company confirmed that Hilton was one of the customers whose account was cancelled, and that Lohan was one of the celebrities whose voicemail was broken into.
Some mobile networks use caller ID to identify the caller and remove the need for further security to access voicemail.
However, if the caller uses SpoofCard all they need to know is the victim's phone number to gain full access to their voicemail.
SpoofCard said that it has implemented software controls on its network so that customers can no longer use its service to break into the voicemail boxes of Lohan or the other victims it has identified.
Hilton was herself the victim of a mobile phone hack last year. Hackers stole addresses, phone numbers, personal notes and photographs stored on the celebrity's T-Mobile Sidekick II smartphone on 22 February 2005.
The supposed rivalry between Lohan and Hilton has been widely covered in the tabloid press.