welcome to the forum.

we need a little more information then that if we are gonna help you.

what version of avast you using?

whats your operation system?

what file is avast flagging as malware?

have you tried a boot scan?

http://www.schmahl.net/avastbootscan.php

second do a scan with malwarebytes antimalware.

http://filehippo.com/download_malwarebytes_anti_malware/

download install update and do a scan. don’t forget to remove what it finds. a system reboot might be needed.

good luck and let us know on the progree or if you need more support.