Finally it all depends on AntiSec. We have no idea wich 1'000'001 datasets they published (first 1m, last 1m or random). If they have access to all 12m UDIDs + the additional information (Country, Postal code, Addresses) they could at least release some statistics about it, this would make it a lot easier to find a (potential) source. (E.g. If we knew wich percentage of the UDIDs came from Europe etc.)