This bug affects the local time function during the daylight savings time change on Windows-based systems. Computers running Windows 95, 98, or NT 4 will delay the one-hour time change for a week in 2001, from April 1 to April 8. The problem has already been fixed for the upcoming Windows 2000 operating system.
"The problem is caused by the Visual C++ runtime library being confused and assuming that daylight savings time doesn't start until April the 8th," explained Smith to the mailing list.
"The confusion appears to be caused by the fact that April 1 falls on a Sunday in the year 2001. The same bug occurs in other years where April 1 also falls on a Sunday," such as 1990, and 2007, according to Smith's email post. He could not be reached for further comment.
Microsoft has confirmed the existence of the bug but says it believes that any actual problems resulting from the glitch will be few and far between.
"This has been blown a little bit out of proportion," said Chris Hargarten, a product manager with the Visual C++ group. "For daylight savings time on April 1 we failed to calculate the one-hour time difference for one week's time. An application that uses a specific function called 'local time' will be affected."
Although Smith traces the problem to a specific file library, Microsoft contends that the presence of the library alone is not enough to trigger the bug. "Not every application that uses this certain [library] uses the local time function," Hargarten said.
Calendar-related glitches like these, while rare, can wreak havoc with applications that depend on certain time-sensitive functions, like hotel wake-up call services. A similar bug which can throw off the date on Windows 98 computers was confirmed last summer.
Microsoft will post information about the problem to its Web site in the next few weeks, and is working on a patch. At this time, the company has no estimates of how many people are affected.
"We've got two years [to fix the bug]," Hargarten said. "We have bugs all the time, and we take them very seriously. We have the processes in place to take care of this."