UK police are looking into complaints about excessive phone bills, allegedly caused by PC software that secretly dials up premium rate numbers.
Some diallers can install themselves automatically
The National Hi-Tech Crime Unit was approached by the premium rate watchdog, Icstis, following a rise in complaints of net-related phone fraud.
"We are in discussions with them," an Icstis spokesman told BBC News Online.
Programs called diallers can secretly install themselves and automatically connect to premium rate lines.
Pay per view
Diallers are commonly used by pornographic or gambling sites as a way of charging people, without the need for a credit card.
But it seems that many people are not aware that they have downloaded a program that will dial a premium rate number.
According to Icstis, the number of complaints about high telephone bills related to web-based premium rate services has soared.
A spokesman said most people thought that they had been hit by a rogue dialler.
In fact, he said, many of the cases were due to people not reading the terms and conditions, or due to someone in the household accessing paid-for content without permission.
But a small number - around 1,000 complaints last year - seemed to involve diallers which had automatically installed themselves on a computer.
In one case, the watchdog has received more than 300 complaints about an adult premium rate number, which it has asked the Hi-Tech Crime Unit to investigate.
One potential issue is that people might have agreed to download a dialler, without been aware of exactly what they have signed up for.
"A lot of these adult sites are not very up front about what they are putting on your computer," said Graham Cluley, senior technology consultant for anti-virus firm Sophos.
"They keep quiet that you are paying for it by your phone bill."
"There are long license agreement that nobody reads. If you have agreed to something, it is hard to complain about it."
People who believe they been fallen victim to a net-related telephone fraud have been advised to contact Icstis.
This problem only affects people who use a dial-up connection to the internet.
But someone with broadband could see their net speeds drop if they still have a modem in their PC.
They are advised to disconnect
the modem from the phone line to prevent a dialler calling a premium rate number.