I suspect it is a combined

virus. I did some search on ddayv.dll and trojan.vundo.b on the web. It seems that in the past, ddayv.dll was always associated with trojan.vundo. The ddayv string is currently not listed as a file created by vundo.b. The possibility is either the Norton detected incorrectly or it's a new version of vundo.b which Symantec has not got a removal tool to deal with it yet. Maybe I should reinstall xp to get rid of it. Have to think it over. Thank you all again for your warm helping hand.