What Are Avira iVDF and VDF files?
The Avira iVDF update is the incremental virus definitions file for Avira AntiVir v8 users only. Avira iVDF is not to be used, if you have AntiVir v9 or v10 of the antivirus program. Avira version 9 and 10 users should download Avira VDF and not the Avira iVDF. You can download the latest Avira updates from their website.
Both formats of the Avira virus definition files (VDF / iVDF) contain the latest definitions to detect viruses and malware and has undergone testing by Avira to prevent false detection, aka false positives. It is only recommended to download the VDF or iVDF if the antivirus program can't download or install the detection signature for some reasons e.g. there is no Internet connection, a malware is preventing the download of updates, or you want to install a new and full virus definition, or what others say, "starting from a scratch."
When you download the Avira VDF and iVDF files, they are already compressed and you don't need to extract them to any location. To better explain what is in the downloaded iVDF and VDF files for Avira, here is what they include: the compressed files consist of antivir0.vdf, antivir1.vdf, antivir2.vdf, antivir3.vdf*** and other .dll files that are related to the engines the Avira antivirus program requires to provide the newest engine to detect malware or viruses.
*** Antivir0.vdf is the master virus definition file which is included in the installer of any Avira product so the program has virus definitions to protect a computer after the install of the antivirus program. AntiVir1.vdf file is the monthly virus definition file, antivir2 is the weekly VDF file and then antivir3.vdf is the daily updates of the virus definition. All of these are required to be installed in the Avira program.
Again, you do not need to manually extract or copy the contents of the VDF and iVDF files that you download from the Avira website. The antivirus program includes a feature to install the VDF or iVDF.