The same issue I have. It would be interesting to know how
@Mircom3D does the conversion. I have a feeling there is a further level of encryption, you know, just to frustrate the damned pirates a little more

I tried ACDSee and err...hated it with a vengeance would probably be the best explanation. Can't remember specifically, but something stopped me and I'm usually pretty open to trying out suggested software.
IrfanView, recognises them as Weppy and gives the file info, but only shows a black screen. Putting it onto 'All supported graphics' and only the png files are listed. GIMP refuses to recognise them. Both open other WebP files without issue.