Microsoft has finished work on Service Pack 2 (SP2) for Windows XP, the company said Friday. The software maker now begins the process of delivering the large, security-focused update to users.

The English language version of the service pack will be released first. Other language versions will follow in intervals after the English version becomes broadly available, Matt Pilla, a senior product manager for Windows at Microsoft said. "We will localize this product in 25 languages, that will take a couple of months," he said.

SP2 will be available through downloads, retail distribution and free CDs, as well as on new PCs. For most users, the download will be between 80M bytes and 100M bytes in size and the English version of SP2 should be available on Windows Update in the coming days, Pilla said.

Microsoft advises consumers to switch on Automatic Updates in Windows XP so the download will be delivered to them once it becomes available. New Windows Update technology will allow the large file to "trickle" down to the user's PC and the download can be interrupted and resumed, according to Microsoft.

Enterprise customers will be able to use a network installation package, which Microsoft plans to offer in the coming days. The network installation package allows businesses to control and tailor the installation of the update.

SP2 for Windows XP is more than the usual roll-up of bug fixes and updates. It also makes significant changes to Windows to improve security of the operating system. Analysts have called the service pack a Windows upgrade instead of a simple update.

Changes to Windows XP made by SP2 fall into four main areas: network protection, memory protection, e-mail security and browsing security. For example, the service pack will install and turn on the Windows Firewall, an improved successor to the Internet Connection Firewall. Also, Internet Explorer (IE) users will receive alerts when visiting Web sites that use potentially malicious ActiveX scripts and IE now has a pop-up blocker that is switched on by default.

Also new is the Windows Security Center, which shows users the status of their firewall and antivirus applications.

Microsoft has warned that Windows XP SP2 could break existing applications because of the changes that are made. Earlier this week the company released an update for Microsoft CRM 1.2 because SP2 will prevent the application from running correctly, it said.

The IDG News Service is a Network World affiliate.