Hi henryjl,
It is recommended to use only one resident anti-virus scanner on your machine. You can add a non-resident scanner, when it is compatible with your main scanning application, ClamWin can be a second scanning application you can download to be used alongside for instance Avast. Then you can download various on-demand scanner, for which you download the latest version from the Internet, DrWebCureIt, stinger.exe. Then you have on-line scanners, for instance BitDefender is a very good one.
Here make sure that the online scanner's definitions do not conflict with your resident scanner. It is a fact that Panda and Avast may lead to conflicts. A good aide can be to download the DrWeb hyperlink-pre-scanning plug-in for your browser. With this small browser add-on you can check your links inside a browser against the most recent definitions on the update servers of DrWeb.
Also it is recommended to have the Avast Webshield run inside your default browser, read more instruction how to do this on the Avast home site.
So scanning OK, but establish that the dogs can stand each other,
and the main rule:
do not use two or more resident scanners on a comp!
polonus