if it was for all of ac, it'd have to become closed source, or heres another idea:
IF client version ex: 1104.840 (win/linux) or 1104.1424 (mac) the user couldnt reach the MS.
OR check if MD5 checksums matched release version checksums
IF client version ex: 1104.840 (win/linux) or 1104.1424 (mac) the user couldnt reach the MS.
OR check if MD5 checksums matched release version checksums