Don't mean to be patrosnising at all, in case this is obvious / you already know, but there is something called a "false positive". This is when an anti-virus flags a file, and says, "hey, this is infected" when its not. Depends on the anti virus, files, algorithms etc.
Far as I'm aware Avira is a piece of shit... I've had one report from a user in Germany regarding that exact same message, in February.
Some very quick searching led me to the below, which shows that Avira has a very high tendancy to report false positives:
avira tr crypt.xpack.gen false positive
Below is a link to the Steam / Valve forums with a user reporting that Avira is detecting that Trojan in Gearbox's Bordelands 2 (don't know if you play video games), but that was just one of the first links I grabbed.
Avira - GearBox Borderlands 2
So... as far as I can see / tell, this is a false positive reported by Avira...
This is the exact same information that I provided to the German user.., they added OctaEdit to their exceptions / ignored it and have been happily running it since then.