Close to 100 customers with numbers starting with 4963 are believed to have received bills in recent weeks that list calls to the 1900910080 information service.

The calls were generally made late at night and charged at a flat rate of $13.97.

Telstra Hunter area general manager Chris Cusack said this week that investigators had identified several hundred calls to the number, which is associated with the online game Runescape.

‘‘We believe the calls were made to obtain tokens which are then used to play an online game,’’ Mr Cusack said.

‘‘We have taken steps to prevent any further incorrect charging to the number and are currently identifying all affected customers, whom we will contact as soon as possible and reimburse any incorrect charges.’’

Telstra’s security experts are still investigating exactly how the calls were made.

‘‘We can’t provide further detail at this stage because we expect this will become a police matter,’’ Mr Cusack said.

It is possible the calls were made using sophisticated caller ID spoofing. It usually involves using an internet-based server that can make telephone calls with false numbers.

Surfpin, the offshore company that administers tokens bought using the 1900 service, has denied any knowledge of its service being misused.

‘‘We will be sure to look into this and take all possible measures to ensure our services are not used for such fraud,’’ the company’s customer support service wrote in an email to a wrongly billed customer.