Windows NT - unsupported from end of June

The clock is ticking for those Microsoft customers still using the software maker's Windows NT 4.0 workstation operating system.

Microsoft's telephone support for the 7-year-old operating system ceases at the end of June. Customers' only option will be to go online to work out problems themselves. Until now, the Redmond, Washington-based software maker has kept up its paid telephone, or "extended", support and has developed any needed security patches for the operating system.

Those with the server version of NT 4.0 have a bit more time. Extended support for that operating system doesn't expire until the end of 2004. Extended support consists of paid support and continued security patches known as "hot fixes".

Microsoft had planned to end support for NT 4 Server some time this year but in January, said it would extend the deadline. At the time, the company said more than a quarter of server customers were still running the OS, which made its debut in 1996.

The software maker is hoping that NT 4.0 Server users will move to the company's new Windows Server 2003 operating system, released earlier this year.

Meanwhile, Microsoft on Thursday released an improved version of its Windows 2000 software, including security fixes as well as support for USB 2.0 and wireless internet connections.

Another deadline looms for desktop customers running Windows 98. Extended support for that product ends 15 January.

With its newer operating systems - Windows 2000 Professional and Windows XP - Microsoft has announced an even longer support cycle. Under the new guidelines for system software released after October 2002, the company will offer mainstream support for five years after the OS is made generally available, with extended support running a further two years.

Microsoft has a timeline for operating system support on its website.

Ina Fried writes for CNET News.com.