If you are using AdMuncher and Avast 5.x webshield is useless. Why Avast does not support AdMuncher? Webshield does not scan a thing when AdMuncher is active. 
Whilst I do agree it’s a shame Avast doesn’t work with Admuncher out of the box, there is a way of getting them to work together, provided you’re confident enough (and tolerate risk) to open a program .ini file. Just search the method in this forum 