Oh, since we're talking about it!
I had the same problem about a week ago – although with the HD mod 3.07f and Avast 5.1.889 (these are old versions, but I deliberately didn't update them for several reasons – I only update the databases in Avast). It happened right after another database update (only in my case, Avast flags HD3Launch.exe). The funny thing is that this file was considered safe for a whole year, and suddenly...! No, the file is actually clean – I checked it in various ways. And, since we're talking about old versions, I didn't post here: I thought it was just me having this problem, and the mod itself is fine. I also fixed it by adding HD3Launch.exe to the exceptions.
dnaop-wr, I think about switching to a "better" antivirus from time to time, but I don't want to install them one by one and test them: there are about 30 well-known ones! (see the list on https://www.virustotal.com/ru/) It would take a lot of time, and all sorts of problems might arise. I know one thing: there is no absolute protection and no perfect antivirus; each has its own advantages and disadvantages. Avast suits me because it bothers me the least (there were practically no false positives in a year) and doesn't "overload" the system. I haven't decided what to replace it with yet. As for the firewall (which is also needed, in addition to the antivirus – if you don't have a combined solution like "*** Internet Security"), I can confidently name the best one: Comodo (both according to reviews and tests). No program will access the Internet without your knowledge!