I am using Avira Free Antivir. I just upgraded from version 9 to 10. I've never been able to get the virus update files from Antivir, using the "update" feature of the software - it just doesn't ever come back from "checking for updates." So I get the updates from Softpedia (or elsewhere) once a week, and do a manual update. I've been getting the ivdf_fusebundle.zip files, and then renaming them to vdf_fusebundle.zip - so the Avira software sees it, and the update works, and it updates the dates.
I just read on the Avira website that the ivdf... files are for version 8 and older, and for version 9+ use vdf... files. Have I been using the wrong updates all this time? I can't find those vdf... files anywhere. I don't see them on Avira's website - you apparently have to get them from there using the update feature of the software - but again - that has never worked for me, not with version 9, and not with the new version 10.