I have had a problem with avast.  This might not bother any of you at all. 
Avast works very well and updates automatically.  If you however want to 
uninstall avast, no matter what I did, it prevented my talking dos boxes 
from working.  I mean, uninstall, manually editing the regestry, using a 3rd 
party uninstaller, everything.  It left something behind that blocked 
dectalk express from communicating with it's com port at dos.  No problem at 
all anywhere in windows.
I had to go back to avast, since their was no way to fix this problem.  I 
use my talking dos boxes maybe 5 times a day.