Criminals are defrauding at least 80 people every month by rerouting their dial-up internet connections to offshore locations and running up large phone bills.connections

The two biggest internet firms, BT Ireland and Eircom, released the figures yesterday as they issued advice to consumers to help them avoid the scam, which is known as "modem hijacking".

One incident of fraud highlighted by BT Ireland involved calls that were rerouted through a satellite phone number last month at a cost of €4 per minute.

The consumer had accumulated a bill of €1,000 before the fraud was detected by the company.

The fraud is based on "modem hijacking", whereby internet hackers based in offshore locations re-route a computer user's telephone link to the internet.

The fraudster can then claim a portion of the cost of this telephone call, which is usually charged at rates of up to €5 per minute instead of the typical charge of one to five cents.

Under current regulations, telephone firms should pay any bills that are amassed due to modem hijacking fraud.

But it can take a long time to detect a fraud and consumers must prove they didn't download the dialler on purpose.

Fraudsters reroute a person's internet connection by installing rogue software onto consumer's machine without their knowledge.

This software is often installed automatically when a person clicks onto a particular website or attempts to download from an unreputable website.

The most common type of websites which use auto dialler programmes are adult sites or unofficial music download sites, which use it as an alternative payment method to credit cards. But many websites install the dialler without a user's knowledge.

The fraudsters generally base their "modem hijacking" operations in foreign locations where it is notoriously difficult to pursue the culprits in the courts.

About 400,000 consumers and businesses that use dial-up internet services could fall prey to this form of fraud.

People using broadband cannot fall victim to "modem hijacking" as they have an "always-on" connection to the internet at a flat rate.

BT Ireland receives 50 complaints a month about "modem hijacking" while Eircom receives about 30 complaints per month.

The Commission for Communications Regulation said it was constantly reviewing the situation to determine whether it should reintroduce a ban on direct-dial calls to certain locations which the fraudsters use to reroute the calls.

The ban was in place for several months last year but was lifted earlier this year.

To help combat the fraud, BT Ireland is making free software available to consumers that can stop a computer from dialling higher-cost premium rate or international numbers, even when a rogue dialler is present.

Eircom has also posted information on other free software to prevent modem hijacking on its website at www.eircom.net.