Quite a number

vnunet.com: Over 180 million computer users have downloaded Windows XP Service Pack 2 (SP2), and Microsoft said […] that it is working to make life more secure for those using non-XP systems.

Microsoft released SP2 in August last year. Quite a number of people (and businesses) didn’t upgrade automatically via Windows Update amid concerns primarily from IT professionals on about deploying the service pack in companies, mostly to do with application compatibility and other issues.

So Microsoft provided a way to set a Windows registry key so that the system skipped downloading and installing SP2 but still got any other critical updates.

That blocking mechanism expired in mid April, and Windows Update now delivers SP2 regardless of the registry key.