On May 8th, 2018, development group Splyse began airdropping its new Master Contract Token (MCT) to NEO addresses that had received a transfer of any existing NEP-5 token on the NEO MainNet before May 8, 2018 00:00 UTC (ending with MainNet block 2,240,482).
For more info, read here: https://neonewstoday.com/development/splyse-airdrop-master-contract-tokens-to-nep-5-users/