By James Helm
BBC Dublin correspondent
Direct dial phone calls from Ireland to 13 other countries are to be blocked because of an internet fraud.
Some customers discovered calls to Mauritania on their bills
Hundreds of Irish phone users have run up large bills due to auto-dialling fraud or modem hijacking.
About 350 customers have complained their bills included unfamiliar calls to a number of countries in the South Pacific, and Mauritania in Africa.
One business discovered it had inadvertently run up a bill of nearly 12,200 euros (£8,360).
It is a complex but lucrative fraud. The criminal installs software on computers without the knowledge of the user.
The settings of that computer's internet dial-up are altered, so that when the internet is dialled up, it rings a foreign and highly expensive number.
A portion of the cost of that call can then be siphoned off by the criminal.
In response, Ireland is now to block calls to the Cook Islands, the Solomon Islands, Mauritania and others as its communications regulator tries to stop the fraud.
A spokesman for the regulator called the action "exceptional", and that it was necessary due to an upsurge in complaints.
Anyone who wants to make a legitimate phone call to one of the 13 countries must now make a special request to do so.