Galaxy S4 - i9505 sim free generic handset

[mysticmeg]

So... I've got a i9505 sim free handset that's not been modified in any way software or hardware at all. Running the stock original samsung touchwiz software. I've updated it using OTA perfectly fine in the past but I've just tried checking for updates on my handset through OTA and it says ''Your device has been modified. Software updates are not available'' I mean what the heck is that supposed to mean and how the hell does samsung check to see if my phone is modified when I've never ever rooted or modified the damn software on my handset ever since day one it launched!!!!!!!