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When this was first released in June 2008 [windowsteamblog.com] it was an "optional" update, which requires users of XP to select the update for installation. Is it possible that you selected this update at some point? Restoring to a point previous to this update would most likely solve the problem.
This KB article has some more information about what the package entails. I didn't see any specific information about reverting this package.
Provided you can identify the correct KB... value (looks like KB940157 to me) you should be able to uninstall it. If it is not available as an uninstall option, proceed as follows...
I have never tried this myself so I can offer no assurances as to safety.