I don't know if your problem is solved one part of it is solved the WSC part for sure, but not the other supposed microsoft pop-up.
Are you still getting it and if so please post the full text of the warning (or post a screenshot of it) ?
avast's VPS updates are automatic and once one has been done you will be notified of it. I don't allow auto update (on dial-up) so my Program Settings, Update (Basic) is set to Ask, if one is available it will be notified by a small alert box at the bottom right of the screen that an update is available.
You can also do a manual check/update, right click the avast icon, Updating, iAVS Update, that will either download any available update or tell you you are up to date.