The watchdog said it has received complaints from thousands of dial-up internet users who have been affected by Trojan horses which have silently embedded themselves in PCs before taking over modem connections and routing calls to expensive premium rate overseas numbers, instead of the usual freephone ISP codes.
Graham Cluley, senior technology consultant for Sophos, commented: "Ireland has taken a bold step to protect consumers by suspending calls to certain countries, it will be interesting to see if other European operators will follow suit to protect their users."
Irish telephone users who wish to telephone the 13 countries, most of which are tiny islands in the Pacific Ocean, will be able to request that specific numbers are unblocked.
The countries on the Irish 'banned list', which comes into force on 4 October 2004, are those said to have been named in the majority of complaints. They include Norfolk Island, Nauru, Sao Tome and Principe, Cook Islands, Tokelau, Diego Garcia, Wallis and Fortuna, Tuvalu, Comoros, Kiribati, Solomon Islands, Mauritania and French Polynesia.
In June, the UK's telephone regulator ICSTIS reported a significant rise in complaints about rogue diallers, forcing it to ask the National Hi-Tech Crime Unit (NHTCU) to investigate.