Hundreds of businesses across the West Midlands could be leaving their computer systems open to attacks from devastating viruses by using out- of- date Microsoft technology.

As many as 40 per cent of firms across all industry sectors could be affected, according to IT experts at Coventrybased Alliance Technical Support Services.

But they say that simply reviewing and upgrading workplace IT systems would reduce the threat substantially - and is much easier to do than many bosses think.

Ian Jackson and Julie Eyre, directors of Alliance, said USbased Microsoft stopped its support for Windows NT 4.0 products, the operating system on which many companies run their business, in January (2005).

Windows Server 2003 is the new standard and IT specialists at Alliance - a Microsoft Certified Partner - said switching over was a simple but crucial process for companies which would guard them against data loss, create a central and secure place to store critical business data and save time and money by reducing IT problems.

Mr Jackson said: " Hundreds, if not thousands, of businesses across the region still operate the NT 4.0 server operating system to access business critical software such as accounts packages, but they will no longer have support and protection from emerging threats.

"New viruses carry very clever payloads and could have a potentially devastating effect on older systems as there are no longer any updates available to guard against new threats. This affects all types of industry, from manufacturing to retail and professional services."

Mr Jackson said other benefits of using Windows 2003 Server include being able to link branches of companies together very cost effectively, connecting offices so they can share information with each other in real time and work on their own files from any office or even at home.

He added that many businesses had remained happy to continue using the old NT 4.0 technology without realising the potential dangers and stressed the importance of keeping up to date with the latest developments to avoid pitfalls.

"NT 4.0 was designed in 1994 before the internet was readily available," said Mr Jackson. "NT 4.0 was new then, but it lacks support for modern technologies now and that's one of the fundamental reasons for moving to a new system. Most software currently being released will not work on Windows NT 4.0.

"We are more than ten years down the line and one month in the computer industry can see huge amounts of technological developments. Business should have upgraded their systems years ago.

"If a server died we could possibly retrieve information, but companies should really be writing their systems off after about four years and moving onto new technologies which are more compatible."

Alliance Technical Support Services was formed in 2002 and specialises in providing comprehensive support across the Microsoft product range.

The company recently merged with Coventry firm Purple Mouse. Purple Mouse's managing director Mandy Sutton joined Mr Jackson and Ms Eyre as a director of the newly merged company.

Mr Jackson added one of Alliance's core skills is helping companies migrate from their old systems to new ones with minimum disruption to their day- to- day business operations.

He said: "Changing over can take anything from a week to six weeks depending on how big the system is. If necessary we will work out of office hours to ensure there are no disruptions to business for our clients."