i have heard some saying there are groups but you should be aware no one will share for free beware of scams not all groups are good
Is there a list of those groups that could be dangerous?
I don't know if there is a such list, but there should be. The list will be long though. I recently browsed some of the biggest groups and groups of the most popular cryptocurrency projects. Many of them are infested with spam and scam accounts. So, be very very aware what group are you joining and what is the purpose, what are you looking from there.
If you are looking into an ICO and want to get to know them, then awesome. Telegram is good for that. Again, be sure it is the right group you are joining. There are fake channels as well, that act like the real one, but they are really just luring you in to get your money.
Also, there are groups on Telegram who are just chatting about crypto, the market situation, about different projects and so on. One of those is
https://t.me/cryptofinance24. Everyone is free to join and lets chat about crypto and blockchain.