Again, I'm just a home user, but looking at the Avast! range, the products advertised for small and home office are Endpoint Protection and Endppoint Protection Plus. I haven't actually seen any advertising suggesting that Avast! Internet Security 2014 is for other than home use.
Regardless of that, if the stipulation "Using avast! services without further permission for professional, commercial or promotional purposes is prohibited" appears in the particular product Eula, then I doubt it can be used legally for any business purpose. This is something perhaps needs to be clarified by Avast!