To modify a past block, an attacker would have to redo the proof-of-work of the block and all blocks after it and then catch up with and surpass the work of the honest nodes. We will show later that the probability of a slower attacker catching up diminishes exponentially as subsequent blocks are added.
I found logic bugs that allow audio or video to be transmitted without user consent in five mobile applications including Signal, Duo and Facebook Messenger https://googleprojectzero.blogspot.com/2021/01/the-state-of-state-machines.html
Banks must be trusted to hold our money and transfer it electronically, but they lend it out in waves of credit bubbles with barely a fraction in reserve. We have to trust them with our privacy, trust them not to let identity thieves drain our accounts. Their massive overhead costs make micropayments impossible.
This is a great read. Respect what Satoshi Nakamoto has done for the world, but no one is perfect.