The long-awaited millennium bug turned out be a non-event for information technology departments as Ireland entered the 21st century.

Hundreds of additional staff worked through the night in the major utilities, banks and Government departments throughout the State. There were no instances of systems crashing because of the millennium bug, but all the systems are continuing to be monitored.

Eircom, however, had congestion problems around midnight on New Year's Eve as the network struggled to accommodate more than three million calls over three hours. Emergency services in particular experienced a huge increase in traffic. A spokesman said it was very pleased with the smooth changeover.

"People were either bored mindless or dropping the odd bottle of champagne. Of course, we're still conducting tests and monitoring systems ahead of the return to work on Tuesday. We'll continue to watch things closely until February 29th, when the Leap Year has been predicted to cause system failures," he said.

The ESB also recorded no Y2K alerts. A number of its critical systems had been moved forward to operate in 2000 before the date change. A spokesman said the pressure on the network's capacity was lower than last year, probably because of mild weather.

Dublin's chief city engineer, Mr Michael Phillips, said the water, sewerage and traffic systems had passed through without a glitch. "We can breathe a sigh of relief now and feel reassured the work we have put in has paid off. The next thing we will look to is the effect of the Leap Year, but this has been very encouraging."

The financial services community, which probably spent more money on the Y2K problem than any other sector, also had a smooth transition, with no reported incidents of problems with cash machines or credit card transactions.

By noon on New Year's Eve AIB had already tested its credit cards in Australia. The Central Bank participated in Europewide testing. Yesterday a Central Bank spokesman said the pan-European payments and settlements system had been successfully tested and was expected to run smoothly when business resumed this morning.

The Irish Bankers Federation was also monitoring developments, and says it will be closely watching as systems begin working at full capacity from tomorrow. A spokesman said the Y2K effort and investment made by the banking community were considered necessary and essential. "There was never any sense this was a false alarm. It had to be treated seriously." One Y2K specialist warned of complacency immediately following the date change. Mr Patrick O'Beirne, of Systems Modelling, predicts varying degrees of administrative problems within organisations, but they are most likely to be handled internally and discreetly.

"I think we can expect a number of small and medium-sized businesses will be doing some unpaid overtime to cover their tracks. If customers start being inconvenienced they will know all about it," Mr O'Beirne said.

A virtual plague of malicious millennium viruses had been predicted to crop up around the critical date, but there are no reports of any serious developments.

According to Mr Alec Florence, of the anti-virus company, Priority Data, no virus alerts had been issued. Although there are a number lurking, there were no more than usual.

Mr Florence warned people to be vigilant over the next few weeks, and not to open Microsoft Word attachments sent via email automatically unless the recipient was sure of the sender.

A number of the major banks closed down their email systems over the holidays to avoid such viruses. They are streaming all company email through stand-alone computers where every message can be monitored.