Avira routinely reports independently-developed, clean installers as viruses or trojans. The Avira developers know and don't care.
They do accept submissions of "suspected false positives" from their users and may add submitted files to their whitelist. I would appreciate it if any Avira-using Slime Forest players choose to submit SFA installers and updaters, although if past experience is any guide, this will only prevent false positives until the next new version of SFA is released.
Other free anti-virus programs are available without this problem, such as AVG and Avast.