Recently I introduced Bitcoin and cryptocurrency to my friends and family,they liked the concept but they asked me a question that I wasn't able to answer.Is Bitcoin really secure?What if a hacker was able to hack Bitcoin system/blockchain?Who manages Bitcoin security and what are the security measures taken to avoid hackers being able to steal Bitcoins?Why Bitcoin is not blocked for those who use it illegally by buying/selling in the deepweb market?What if governements ban Bitcoin because of these people?
I really appreciate if you guys give me some answers
If someone wanted to hack bitcoin the only thing they can do is take the coins from the last few blocks that they previously spent. Later there will be an attack on the anyone can spend vulnerabilty of segwit though. That will happen years from now when there is a lot of BTC that have used segwit transactions.
A miner who is big enough can do these things, and so far almost nobody has ever done it because it would go against them and drop the bitcoin price. But years from now when there are millions of BTC in segwit anyone can spend transcations, I am sure miners will attack it then.
https://bitcoincore.org/en/2016/10/28/segwit-costs/#avoidance-2