A new law requiring daylight savings time to start March 11, three weeks earlier than normal, threatens a widespread, Y2K-like computer glitch in U.S. computers preset for the later start date of April 2. In its extreme, security analysts say the glitch could cause a traffic accident or a train derailment. "It is always the unanticipated system that nobody knew about or realized was important that will become significant," says ABC News consultant Richard Clarke, the former White House counterterror and cyber crime chief. THE BLOTTER RECOMMENDS Blotter Top 7 Most Outrageous E-mail Hoaxes Blotter Hundreds of FBI Laptop Computers and Weapons Missing, IG Audit Shows Click Here for to Check Out the Latest Brian Ross Slideshows "Traffic lights and switches on train rails are two candidates that could cause an accident," said Clarke, who also said bank vaults will be open an hour later, and travelers might miss connecting flights in Europe if schedules are off by an hour. He does not anticipate accidents involving planes since air traffic controllers will still see the planes. The upcoming computer glitch is reminiscent of Y2K, but security analysts don’t fear the disasters that might have happened if computer systems stopped functioning when the year 1999 changed to 2000. "The difference between this and Y2K is that systems continue to work, they’re just an hour off, whereas with Y2K we had reason to believe that systems would stop working," said Clarke. Click Here for Full Blotter Coverage. Still, technology analysts say that companies should have anticipated the upcoming time change and tested the patches for computer software and hardware systems long in advance. "U.S. businesses are at fault for waiting until the last minute to patch and test their systems. On a scale of one to five, in terms of preparedness, [U.S. companies] are a two," says R "Ray" Wang of Forrester Inc., an independent technology research company. In addition to transportation industries, financial services, telecommunication, health care and high-tech manufacturing companies are most at risk because of their precision-time nature, according to Wang. Many companies are now scrambling to patch software to avoid any problems, but most have not yet loaded the Microsoft patch, according to Clarke. This week, the Walt Disney Company, the parent of ABC, sent a memo to its employees warning of possible problems with the imminent changes, "While good for the environment, this legislation underestimated the impact to computers." The memo warned that meetings on Microsoft Outlook calendars may display incorrectly, and Blackberry and other hand-held devices may be temporarily "out of sync" with desktop calendars while patching occurs. The daylight savings time extension is part of an energy bill passed in 2005 in an effort to cut back on the use of electricity.