Microsoft has officially released its security-oriented Windows XP update, Service Pack 2 (SP2), to manufacturing, and said the update would become available to IT managers, consumers and PC makers starting next week.

But while Microsoft is urging upgrades as soon as possible, IT managers contacted by Techworld say they are in no hurry to install SP2, which amounts to a new operating system, they say.

The update is designed to improve Windows security - and Microsoft's reputation - through extensive changes to Windows XP's default security settings, new security tools and a new patch management system. Because of the scale of the changes, which Microsoft admits are likely to break many existing applications, businesses say they are putting the service pack through a more rigorous testing procedure than usual. "We are treating this as an OS upgrade," said an IT director at a major international IT company.

Despite the release to manufacturing, which marks the completion of the software, even the most adventurous of users may not see SP2 for months, Microsoft said. The package will be distributed through Windows XP's online update feature, or via free CDs, installation by retailers and on new PCs, Microsoft said, while enterprise users are most likely to receive the update from their company's own servers through a centralised installation process.

Enterprises will face the longest process for getting SP2 up and running, and will be first in line for the software: IT managers will have access to SP2's full 256MB starting next week, Microsoft said. Most PCs will not need the full package; those with SP1 and up-to-date patches, for example, will need less updating. Microsoft estimates that XP Home Edition installations will face an 80MB download, on average, while XP Professional desktops will have an average 100MB download. If the PC doesn't have SP1 installed, it will add 20MB to the download.

Microsoft is urging users to switch on XP's Automatic Update feature, which downloads patches in the background, and expects to distribute SP2 to about 100 million PCs via this method in the next two months. Users who want to download the service pack manually will be able to do so by the end of August. Finally, new PCs with SP2 preloaded are expected to appear beginning in September and October.

Users outside North America, or those using languages other than English, can expect to wait longer for SP2, Microsoft said; the company is localising the update in 25 languages over the coming two months. Heavy demand on the Internet may create additional delays.

Microsoft is describing the service pack as a quantum leap in PC security and is urging consumers and businesses to roll it out as soon as possible. "This is not about fun and games," Barry Goffe, a group manager in Microsoft's Windows group, told IDG News Service. "SP2 is about improving the security of our customers' infrastructure. We have spent a lot of time making sure that this delivers a lot of value to all our customers. We're urging all customers to deploy SP2 as soon as possible."

However, IT managers are in no hurry. IBM sent a memo to workers advising them not to download the service pack until compatibility testing had been carried out. Sophos Antivirus told Techworld that, while it expects SP2 will improve security, it has no immediate plans to deploy the service pack internally. "There would be no advantage to Sophos in trying to roll it out on the day of its release," said a company spokesman. "Sooner or later Sophos will have to roll out Windows XP SP2 - it's just not something we consider a very high priority presently, and we will only do when we are confident the time is right and we can do it properly."

Another major IT firm said it would deploy SP2 after "extensive" quality assurance, but expected problems to arise nevertheless. "There will be some inevitable compatibility issues that are missed in QA. There will also be issues with the SP2 itself and we fully expect Microsoft to follow-up with fixes," the company's IT director said.

Many companies say they would like the benefits promised by the service pack, but haven't yet made the switch to XP - a common situation in the enterprise, according to industry analysts. Sophos said it has very few XP PCs running in its UK headquarters. "To this day at my company we're putting Windows 2000 on all new computers and we're not about to change to XP anyime soon," said a tech worker at another company.