From what I know, autorun.inf is the file associated with the AutoRun function on your computer... say if you insert a CD or USB flash drive, your computer is typically set as a default to run/open them automatically. Disabling the AutoRun function can protect your computer from other kinds of attacks. I saw the link below posted elsewhere on BC, it might help explain further. It discusses the AutoRun feature, and why it is best when disabled:http://miekiemoes.blogspot.com/2008/11/ple...torun-asap.html
I've never used Avira but it may be a new(er) function that was added for your protection. If so, I am sure there is somewhere within Avira's settings where you can disable that function, if it is that bothersome to you, although it's probably better left how it is, as the link above should explain in detail.