Microsoft has urged the quarter of a million Irish users of its Windows XP operating system to install new software that is designed to increase security on their home computers.

It has also asked corporate customers to evaluate the software package in a test environment to see how they can install the update without causing problems with existing computer systems.

The US software giant said it was making the security update available to global users of its latest operating system on CD or via a download from the internet. It expects to distribute 100 million copies of the update globally within the next two months.

The update, which is called Windows XP Service Pack 2, is the most significant launch of security features by Microsoft since it launched its trustworthy computing initiative last year.

This initiative was introduced by Microsoft founder Mr Bill Gates, following a spate of security breaches against Microsoft software, which have severely tarnished the firm's reputation and cost customers billions of euro.

The new service pack includes a range of new features designed to prevent computer viruses and worms infecting both corporate and home PC users' systems.

Once installed on a user's computer, the software will switch on an existing firewall facility within Windows XP that is not widely used by home users as it was not made a default at the launch of the operating system.

The software pack includes a new tool to manage the downloading of attachments from emails, one of the most common ways for transmitting computer worms and viruses.

It also includes tools to manage irritating pop-up windows that appear when customer's click on to certain websites.

These pop-up boxes, which are typically advertisements, could potentially install unsafe software code onto a computer, says Microsoft. The update will also provide users with a new application to manage security called the Windows Security Centre.

This will become available in the Control Panel section of Windows XP and should automatically prompt a computer user when a particular security feature is turned off.

Mr Clive Ryan a group manager at Microsoft Ireland, said it was important that IT managers in companies evaluated the new security pack in a test environment.

He added that certain business applications may be affected by the update and a full list of potential issues were available on the Microsoft website.

Home users of Windows XP could find that certain applications that they have downloaded from the Web, for example freeware games, may not run properly after the upgrade.

Mr Ryan said that there were currently around 250,000 home users of Windows XP in the Republic.