Thousands of companies and individuals could face security headaches and inconvenience as Microsoft stops selling some of its older products.
It has announced it is withdrawing products such as Windows 98, Windows NT 4 and Outlook 2000.
The decision was made because the programs contain code outlawed under a legal deal with rival Sun Microsystems.
But a survey has showed that most organisations with more than 10 computers still use older products.
Remove and replace
The survey was carried out by US firm AssetMetrix. It found that 80% of the organisations it questioned were still using Windows 98 and 95.
Inside those firms, 39% of machines were running the venerable operating systems.
By contrast AssetMetrix found that only 7% of the PCs companies were using had the latest Windows operating system, XP, installed. Windows 2000 was the most popular operating system.
The survey covered more than 375,000 machines in 670 companies some of which had up to 49,000 PCs in their organisation.
Microsoft is stopping selling Windows 98 and many other products and operating systems because of an agreement it reached with Sun in January 2001.
That agreement came out of a wrangle over the licensing of the Java and has led Microsoft to stop distributing and selling products containing the disputed version of the language
In some of its other products Microsoft said it would remove and replace the offending Java code.
For many Microsoft customers, free support for Windows 98 ended earlier this year as the product reached a key point in its lifecycle. Many third-parties still offer paid support for these products.
From 16 January 2004 anyone looking for help with Windows 98 will be forced to consult Microsoft’s online help pages or look elsewhere for aid.
The news also means that Microsoft will stop producing regular security patches for Windows 98 which could mean problems for firms that use it extensively.
In a statement Microsoft said it would evaluate threats to the software and produce patches as needed.
Windows 95 has already been declared obsolete and officially reached the end of its life on 31 December 2002.
BackOffice Server 2000
Embedded Visual Tools 3.0
Office XP Developer
Office 2000 Developer
Office 2000 Tools
Office 2000 Multilingual
Office 2000 Premium SR-1
Office 2000 Service Pack 2
SQL Server 7
SQL Server 7 Service Pack 3
Windows 98 (does not affect Windows 98 Second Edition)
Windows 98 Y2K
Windows 98 Resource Kit
Windows 98 SP1 (does not affect Windows 98 Second Edition)
Windows NT 4.0 (Terminal Server and Option Pack add-ons only)
Visual Basic for (Alpha Systems)
Visual Studio 6 MSDE
Visual Studio 6.0 SP3 and SP5