Hi puffpuffapfel,
I do not speak German, thus I will assist you with your issues and DJBone will translate.
If I understand, you are receiving avast!'s warnings? Can you attach the screenshot of that warning?
You have only posted the primary FRST.txt logfile, where is Addition.txt? Please run FRST again, wait for tool to update, check box for Addition.txt and preform fresh Scan. Please, post me fresh both, FRST.txt and Addition.txt logfle as I need both logs for analysist.