it can’t really: ANY file has to be downloaded before scanning, even if an AV uses some sort of Proxy/Internet filter

but the other 3 still can download with no Virus Warning.

This is probably because they are archives which avast’s AV-Shield doesn’t & shouldn’t scan…
Read in the User’s FAQ on how to enable archive scanning for the Resident Shield ( = On-access)
→ “DefTasks.xml - Scanning archive files…”:
http://forum.avast.com/index.php?board=9;action=display;threadid=4818;start=15

But this
a) is really unnecessary
b) can slow down your computer quite a bit…

:wink: