Lots got banned, trying to get new GUID to get past it. I'm guessing their IP may be able to be matched to their old banned GUID by the guys running DayZ or something like that, and they don't want to be banned again assuming they figured out how to change the GUID properly.
I'm not sure this is even working for OA tho, nobody seems to want to confirm it. OP says they don't think it'll work, and there's a few posts a page or two back that send mixed messages. I've managed to change my GUID fine, it's just not valid as I'm using a keygen and I'd assume all the keys work fine for single player but they were blacklisted for multi or something along those lines.
Few more days and I'll just buy OA again and stick to the CE inf ammo trick. Damn the server bombers for making me miss out on a weekend of dayz.