It seems that there are widespread problems with this latest update interacting with third-party antiviruses.
I know it may be too late, but I recommend you don’t update just yet if you haven’t (always wait at least a week, just to be sure). Delay that update if you can on all version of Windows.
And if you have updated and have problems, it seems that Safe Mode still works, and you can then uninstall the update from there. If your computer seemed fine, but runs slower afterwards, try this.