re: Why bitcoin is worse than a Madoff-style Ponzi scheme

Bitcoin, as in the blockchain ledger, cannot be hacked with current computing power. Quantum computers may have that ability some day, but people are already working on ways to update the cryptography to be quantum proof.

The bitcoin network can theoretically be taken over with a 51% attack, but the odds of that happening are less and less with each passing day.

Personal bitcoins can be stolen through exchange exploits or phishing scams. Mt Gox being the most famous.

Other cryptocurrencies have vulnerabilities, through smart contract exploits, but those exploits are specific to those smart contracts and not the blockchain themselves.