My questions are regarding the level of security endowed within Bitcoin.
Has there ever been a 51% on Bitcoin's network? I understand that as more miners enter the network, the greater the hash rate meaning the more difficult it is to perform an attack. This also means that it was much easier to perform the attack during the early years of Bitcoin, that's when it was most vulnerable. Was there any attack in the early years of Bitcoin and how much would it cost now to perform a 51% attack?