The daily updates of the VDF file are not downloaded in form of one single VDF file but of one small VDF file (Name: antivir3.vdf) of only a few kilobytes, which only contains the new virus signatures.
This daily VDF file supplements the weekly VDF (Name: antivir2.vdf), the monthly VDF (Name: antivir1.vdf) and the so-called basic VDF (Name: antivir0.vdf), which are installed on every AntiVir program package by default.
If one of the mentioned VDF files reaches a determined size, its content is transferred to the next higher VDF file, which has to be downloaded too.
The incremental VDF process has the advantage that the download volume is extremely small. This leads to very small download times and costs, also if the download is carried out via an Internet modem connection.