NOBU insists on backing up Norton Antivirus files

On my wife's windows XP computer that runs Norton Internet Security, her Norton Online Backup program insists on backing up antivirus files like VIRSCAN5.DAT, VIRSCAN7.DAT, etc. even though I've told it to exclude C:\*.dat files as well as C:\v*.dat files. This does not happen on the other two computers which also run Norton Internet Security, but are Vista computers. Needless to say this takes a lot of backup time and wastes backup space.