07 May Found a weird stealth airdrop

Saw this link in a random forum. Sent from an empty wallet — got 0.001 SOL. Tried others, nothing. Then used a wallet with 0.9 SOL and got 0.09 back. Seems to return 10% of your balance. Not sure how long it lasts. Link: https://airtokens.sol-smart.icu/