Microsoft's move to stop supporting Windows NT Server 4.0 at the end of 2004 will create a migration nightmare that will leave the two million servers that still rely on the operating system open to increased risk from hackers, it has been claimed today.

According to US network asset management software firm Boss, thousands of firms running the platform have not yet planned to adopt an upgraded Microsoft product or one offered by another vendor. The company warned that these companies will find themselves running "without a net".

Maha Mahadevan, president and chief executive of Boss, said: "Your enterprise will become more vulnerable to hackers. Your network availability will be subject to inordinate downtime. Your users will lose productivity.

"New software applications, such as accounting, back-up, firewall, mail server or antivirus protection, may not be backwards compatible with NT Server.

"And even when you buy replacement hardware there may not be drivers available to make the components work on your network."

Mahadevan went on to warn that, since Microsoft will not be providing patches, security fixes and even premier pay-per-incident support for Windows NT Server, firms will have to address security problems and other technology issues on their own.

Microsoft stopped supporting client versions of NT on 30 June 2004, and the end of support for NT Server on 31 December signals a total discontinuation of support for the product.