Everyone in the world is free to join bitcoin even if they are criminal, terrorist or thieves. Yes, I've heard from the news. Some of the terrorist used bitcoin as their weapon . Terrorist knows that bitcoin helps them to make money then they used the money that  comes from BTC to buy guns and such. As their source of income, they used bitcoin in a bad way like scamming many people. Well, some terrorist know how powerful is the crypto currency especially the btc. They used BTC by means of doing illegal things that may affect many people in our country.