report false positive here
http://www.avast.com/en-us/contact-form.php?loadStyles

upload suspicious file(s) to www.virustotal.com and test with 43 malware scanners
when you have the result, copy the url in the address bar and post it here for us to see

alternative
Jotti http://virusscan.jotti.org/en
VirSCAN http://virscan.org/
Metascan http://www.metascan-online.com/