This means that people who wanted tomay now be into their systems.
An e-mailed statement from Microsoft said: "On April 12, a tool blocking the download of Windows XP SP2 via Automatic Updates will expire and SP2 will automatically be downloaded."
The company added that small businesses and home users will not be affected by the change.
SP2 was released last year to bolster the security functions built into Windows XP. The main concern of the forced installment is that SP2 automatically enables the operating system's firewall. For many users and system administrators this makes more sense than having it disabled by default, but it also means that if the firewall fails to recognize an application, it could prevent that program from working smoothly.
"Taking away that option could be time-consuming for administrators," said Alan Phillips, director of training company 7Safe. "One would have thought that Microsoft would have performed sufficient testing for this. It will be interesting to see if there are any stories that come out of this."
Microsoft advised companies still looking to prevent the rollout of SP2 to use a patch management tool such as System Updates Services. But some members of the IT industry were concerned that Microsoft had not provided enough information on this.
"It would have been nice to see Microsoft properly clarifying how this works with SUS," said Paul Simmonds, a global information security director at ICI. "So far, I've yet to see any clarification."
But one ZDNet UK reader believes the move will cause few problems: "I have been installing SP2 on many different machines for some time now, in both business and home environments, and have not experienced any problems. I think the scare stories have put people off, but really, in most cases there is nothing to worry about. The benefits far outweigh the possibility of something going wrong."
Dan Ilett of ZDNet UK reported from London.