Police are asking people to check all their notes and coins
Ireland was the only eurozone country that issued every household with an electronic currency converter.
The calculator-like devices were distributed freely through the postal offices.
The converters and relatively high usage of cash in Ireland helped to build the confidence with the transition to euro, the official changeover body said on Tuesday.
Dyslexic forgery
But as the euro has gained in popularity among shoppers, so it has among counterfeiters.
Irish police discovered what is believed to be Europe's first forged euro coin in circulation.
The bogus 1 euro coin was used over the week end in a shop in Castleblayney, in the north east of the country, close to the border with Northern Ireland.
To spot the forged coin was not a problem.
According to police, the coin was of very bad quality, had no serrated edge and was marked "eur" instead of "euro".
Police were puzzled about the motive for counterfeiting the coin, which, because of its low denomination, would not present forgers with large returns.
Italian police confiscated six bogus 1 euro cent coins in Rome on Friday.
Investigators believe the coins might have been minted badly on purpose by someone inside the national mint in order to feed the collectors market
Bigger notes, bigger returns
Three false 50 euro notes were found in pubs in Dublin and one in Celbridge, County Kildare. Police said all were of poor quality.
The fake banknotes were missing a centre silver foil strip and hologram and the foil on the right-hand side was blue instead of silver.
"We would ask people to check all their notes and coins and familiarise with all the security feature," a police spokeswoman said.
Ireland became one of the first countries to discover forged euro currency when a 10 euro note was found on 2 January, just 24 hours after the launch of the new cash.
But false euro notes have also been found in other countries.
Dutch police discovered a plastic bag full of forged 10 and 20-euro notes, some of which were not cut of the paper they were printed on.
In France, a woman and her 21-year-old son were placed under investigation after the woman brought bread with a fake 50 euro note.
Forged notes have also been discovered in Germany and Finland.