Not sure where you got the idea it might have somehting to do with Alcohol or CloneCD, but I believe that the update you are referring to is the update number 811493
811493: Security Update (Windows XP)
Download size: 5.8 MB, < 1 minute
A security issue has been identified that could allow an attacker to compromise a computer running MicrosoftÂ® WindowsÂ® XP and gain complete control over it. An attacker would need the ability to log onto the computer locally to carry out an attack. You can help protect your computer by installing this update from Microsoft. After you install this update, you may have to restart your computer. Read more...
This update has been known to virtually stop a pc dead, and hence it was moved from Critical update to Recommended update. The cause of the slow down has been attributed to running virus checkers which monitor system constantly, ie auto-protect, and m$ were rumoured to have said turn off the auto-protect feature of Virus Checkers (unconfirmed).
Hope that is the one you are talking of, as I haven't heard of any other updates with problems.
 Found the article where m$ tell you basically to turn off your virus checker, you can view it HERE what a great idea, turn off your virus checker so that you can use windows, great security update HeHe [/edit]