UP to 300 internet users a day are being targeted by a computer virus which repeatedly dials expensive premium-rate phone lines.
BT, which revealed it has received more than 80,000 complaints about the con, said it was costing UK consumers around £8 million each year.
The so-called "rogue diallers" can rack up large profits from the automatic calls and the first their unsu
specting victims know about it is when grossly inflated phone bills land on their doormats.
The virus prompts home computers into automatically calling premium-rate numbers at £1.50 a minute, and has left some people with bills of up to £1600.
The system is covertly download on to an individual's PC and replaces the default internet connection with an 090 number.
The new figures show that the problem is still widespread, despite attempts by the industry to raise awareness of the issue and help customers protect themselves.
BT recently announced a free software download that stops a PC dialling a higher-cost premium rate or international number, even if dialler software is present.
Using the system, customers are warned if their modem starts to dial anything other than a list of approved numbers.
Rogue diallers are triggered by closing certain pop-up boxes on premium content websites, through minimising internet icons or the opening of certain e-mails.
The software then becomes embedded, meaning that when internet users next log on, they are automatically connected to a premium rate satellite or international service rather than their usual internet service provider (ISP) number.
Two companies based in New York were recently fined £100,000 each for targeting internet users with the costly scam.
But while other countries have banned "diallers" outright, the UK has been reluctant to penalise the legitimate premium rate service which is worth more than £1 billion a year to the UK economy.
Politicians have urged the industry watchdog, the Independent Committee for the Supervision of Standards of Telephone Information Services (ICSTIS), to crack down harder on the scam.
Since BT launched its free protection software on May 3, it has alerted an average 304 customers a day to the scam.
Called BT Privacy Online, the service sends a warning to customers whose dial-up modem tries to call any number not included on a pre-approved list.
It also sends warning messages to victims' home phones.
In a statement on the ICSTIS website, director George Kidd said: "Phone companies have the systems to identify suspicious call patterns and can take action before their customers unknowingly run up huge bills.
"Those networks that give out premium rate numbers in the first place have a duty to carry out thorough checks on those they give them to and to look at the speed at which they pass money on to them."
