Businesses are on standby for the date-related bug that could hit computer systems today - and Microsoft users could be more affected than most.
Millennium bug taskforce Action 2000 has identified a total of 21 software packages that will not recognise 29 February properly - eight of which are supplied by the software giant.
Action 2000 says a fix is available for most, but that some will need to bereplaced. The full list can be found at www.bug2000.co.uk
They include Windows for Workgroups, Windows 95, Outlook 98 and Windows NT server 4.
A Microsoft spokeswoman said: "We don't envisage any problems because we haven't seen an increase in calls, but as with Year 2000 we're ready for the possibility."
29 February is a potential problem because it is an exception to the leap year rule, occurring once every four years. Years divisible by 100 are not leap years, but those that can be divided by 400 are. This makes year 2000 a leap year with 366 days. It is the first such leap year since 1600.
Computer programmers may not have recognised this when tackling the millennium bug, which could affect the 29 February rollover.
However, in light of the relatively low impact of the millennium bug, computer experts are not unduly concerned, and many companies did take it into account when carrying out Year 2000 work.
Action 2000 said "any system using dates could be disrupted", but does not foresee major problems.
Bob Hammersley, senior manager for IT services at Sainsbury's who managed the supermarket's millennium rollover, said the leap year rule was taken into account in the retailer's Year 2000 compliance programme.
"We have reduced the problem to manageable proportions. Any problems will be dealt with as and when they arise. We will have normal support cover, but there will be a couple of extra people on the service desk in case we have any queries from people in the stores," he said.
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