I know that TON is one of the most talked about crypto project in this crypto space right now and this have also attcated a lot of bad actors too, now TON wallets are receiving many NFTs for free and some do look almost legit, enough to confuse a newbie that it is real, I am here to warm you guys to stay away from free NFTs.
If you don't pay for it, you shouldn't claim any ownership.
Fake NFTs and Tokens can live in your wallet for years without comprising your crypto wallet until you deceid to touch them.
A lesson you should learn from this is do not claim ownership of something that's not yours, in this crypto space nothing is for free.
Follow this procedure.
1. DONT TOUCH
2. DONT CLAIM
3. DONT EVEN ATTEMPT 1 & 2 RULES ABOVE.
Most free NFTs are just scams as you said and if you allow them to access and provide the passphrase on your wallet then they will surely wipe out all of your available assets. And, that is why it is really to be good to be true getting free NFTs.
I would say that some of them are legit and provide NFTs but it is really hard to trust them.