We have implemented this flag, in order to avoid unnecessary download traffic. It can only be set by us, in-house, as we generate the control files through the Update compile.
It means, all files that could not be updated, receive this ignore flag through the Update compiler.
This ensures that the Webloader uses exactly the same control files as the Updater!
[UPD] [INFO] File 'wks_avira/win32/de/basic-nt/avscan.exe' (local, Server): 09.00.03.03 < 09.00.03.05
[UPD] [INFO] File 'wks_avira/win32/de/basic-nt/avupgsvc.exe' has set the IGNORE flag, so it will not be processed.