Neowin sends word that they've posted some information they received regarding low performance after installing the Q811493 hotfix from Microsoft. Basically it involves disabling your Anti-Viruses auto-protection feature.
Would you like to know more?

I downloaded this update and it did slow my machine down some. Rolled back to the last restore point and everything is okay. I'm supposed to leave Norton AV off? I don't think so, I'll just do without this update.

According to Neowin's post, no, just don't have it running in the background.

I'm not sure I understand, not have it running in the background? Does this mean disable it during install/download and then it will be safe to enable it after? Or will I have to keep my NAV disabled (I doubt that is right)? Last question; will Norton Personal Firewall have any effect on the installation of this "patch"? Questions I doubt anyone will have the answers to, but it's worth a try, Thanks.

After rereading the article, I guess it means, off during install. At any rate, I think I won't install that update, at least for now.