Bro, the more hidden they are, the riskier it is for you, Bitcoin and other cryptocurrencies are plain in transactions even if they are decentralised, so the so-called hidden strategy or association is nonsense to me even as their transactions are obvious when they move money, so what? There is no big deal here and for you not to have found them through the search engine means that they are not popular. I do not think this should raise our curiosity for any reason but to forget them and follow the right/best procedures to own, hold and move your coins as you wish.

And please, be very careful about scams on the internet, I have seen similar packages like this where they use invitation to scam people even as they remain hidden when you search for them. But it was in fiat. Since it's USDT, what is the difference? They can come in divers ways. Be careful!