please help, i cant get rid of this ???
Are you using Windows XP?
Can you schedule a boot-time scanning?
Start avast! > Right click the skin > Schedule a boot-time scanning.
Select for scanning archives.
Boot.
Did you try www.ewido.net?
Welcome to the forums, msmolly71099. 
As Tech suggested, it would be helpful if you gave us more information. Such as … OS, security program you already have, where win32:purity trojan is found, complete text (or screenshot) of any warning messages, etc.
Look here for a similar thread,
http://forum.avast.com/index.php?PHPSESSID=ca6c0e82b6393de57b1c4d3822208681&topic=20203.msg169302
Our forum has a good search function.
polonus