That largess, however, doesn't extend to users still relying on even older Microsoft software, namely those products that have rolled off the support list entirely. Windows NT, for instance, which exited extended support more than two years ago, must be modified manually, as do other unsupported apps affected by the DST changes, including Exchange Server 5.5, which left support in January 2006, and Outlook 97, which lost support in February 2002.

Microsoft will not be writing a fix for those products. "It's just too difficult" to support obsolete software, said Sweatt. "It would involve significant" resources and apply to a very small group. Microsoft has previously urged those users to update to newer software.

As an option, Microsoft points some of those users to a support document posted last May and updated again Wednesday, in particular the "tzedit.exe" utility linked from the document. Microsoft states that Tzedit.exe works on all versions of Windows

There are no similar tools for aged Exchange Server or Outlook, however.

Windows Vista and Outlook 2007, released in January to retail customers and in November to business, do not need to be updated, since they were coded after Congress passed the 2005 Energy Policy Act that revised DST's start and stop dates.