In an effort to avoid a repeat of computer glitches that occurred as a result of last year's earlier-than-usual switch to daylight-saving time, Microsoft is warning home and business PC users that their systems may require an update to successfully spring ahead this year.

"Unless certain updates are applied to your computer, the time zone settings for your computer's system clock may be incorrect," Microsoft said in a post that appeared Friday on its Web site.

In the United States, clocks move ahead one hour on Sunday. Many other countries around the world will be switching to their own form of daylight time in the coming weeks. Problems can occur if computers' internal clocks are at odds with the time in the real world.

Thousands of Microsoft Exchange Server 2007 users found that out the hard way last week when the software got flummoxed by the Feb. 29 leap day.

To ensure Windows users aren't hit with a daylight time bug, Microsoft has launched an automated diagnostic and update service on its Web site that installs patches on systems that need them. The service is available for all versions of Windows Vista and most versions of Windows XP, as well as Windows Server 2003.

Updates also are available for Windows Mobile. Some older versions of Windows, such as Windows ME, aren't supported.

Congress last year changed the switch to daylight-saving time by about three weeks, from early April to early March. The move caught many programmers unaware. As a result, tech support personnel had to scramble to update systems in a scenario reminiscent of the infamous Y2K bug.

Los Alamos National Laboratory went so far as to warn its employees that their coffee makers might not function properly. But the glitch caused more than minor inconveniences. Pacific Gas and Electric had to perform emergency updates on thousands of meters in California -- at an estimated cost of $38 million.