Send the sample to
virus@avast.com zipped and password protected with the password in email body, a link to this topic might help andundetected malware in the subject.
Or you can also add the file to the User Files (File, Add) section of the avast chest (if it isn't already there) where it can do no harm and send it from there (select the file, right click, email to Alwil Software). No need to zip and PW protect when the sample is sent from chest. A copy of the file/s will remain in the original location, so any further action you take can remove that.
I don't know where you come up with the low risk trojan categorisation from but trojans can be virtually anything, that is the nature of the trojan something containing an unknown package.
Codec's really are one of the high risk area as there are many hooks out there to say you need a specific codec that you don't have here's a link to get it. Whilst you have exercised care new variants could well get past avast, so another useful tool is
VirusTotal - Multi engine on-line virus scanner if you feel something is suspect, there are currently 36 different scanners there.
What version of avast do you have (the latest is 4.8.1229) ?
From version 4.8 there is a self-defence module, which with a few exceptions is quite good at blocking attacks on avast!
