UK firms that stick with Microsoft's NT4 operating system despite the imminent withdrawal of support run the risk of breaking corporate governance rules, analysts warned last week.

Under the information security standard BS7799, which underpins many newer regulations covering operational risk, firms must use software "maintained at a level supported by the supplier". New IT Week research shows that 18 percent of UK firms still rely on Windows NT as their main server operating system, even though security updates are due to stop at the end of the year.

"Quite clearly firms should opt for vendor-supported software, otherwise they are exposing themselves under compliance rules," said Una Du Noyer, head of infrastructure and security at consultancy Capgemini. "Firms need to work out just how serious the risk is, and weigh it up against the cost of putting it right."

NT4 is even more widespread when non-core server systems are considered ð 77 percent of firms use it somewhere on-site, according to the IT Week/Computing Usage of Server Systems survey of 200 firms, carried out by NOP, and sponsored by Microsoft.

"There is a phenomenal amount of NT still rattling around and it would seem that the end of support is not that much of a worry at present," said Du Noyer. "Most people have had this system for years and cannot remember the last time they have had to contact Microsoft with an issue."

Microsoft is increasing its efforts to move firms to Windows Server 2003 as support for NT draws to a close. In a recent email to Microsoft staff, chief executive Steve Ballmer said the firm must act to change customer perceptions that "older versions of Office and Windows are good enough".

Only 14 percent of firms have taken up Windows Server 2003 as their main server platform, while 40 percent rely on Windows 2000 Server. Nicholas McGrath, head of platform strategy at Microsoft, said there is a steady move to Windows Server 2003 from NT4. "The key drivers are the security and reliability of Win Server 2003," he added.

Elsewhere, the survey found few firms chose Linux for their critical services ð it accounted for only two percent of principal enterprise servers. However, 44 percent said they use Linux in a supporting role.

Given the widespread deployment of Microsoft systems, licensing costs remain the biggest concern for enterprises. Twenty-three percent of firms said that licensing costs are their biggest financial headache, followed by support costs at 21 percent. Half of all firms said that the need to reduce licensing costs of server operating systems is a key objective for the next 12 months.