Antivirus used to only detect virus or files infected by virus, but that meant they were always one step behind since they couldn't detect new virus that were just created.
So antivirus companies started to make their products detect "Threat Files" which are files that the antivirus doesn't recognize and assume it is a virus, even without knowing if it is or not (just to be sure) this is called just like Roy said above "False Positives", most antivirus allow the user to flag or choose to ignore those files if the user knows they are safe and other antivirus even allow the user to send a copy of the file to the antivirus company so they can analyze it and make their product not detect it as a virus anymore if it is not one
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Antivirus usually flag files that are not dangerous if they are .dll or .ini and in this case it looks like it was the BSAsharp.dll I can say that the one included in the installer is not a virus and if it was we would have hundreds or thousands of users telling us it was
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