Vitalik Buterin, co-founder of Ethereum, emphasized in a post that the key security attribute of blockchain is that even in the event of a 51% attack, invalid blocks cannot be made valid, so 51% validators colluding or software failures cannot steal user assets. However, he warned that if validators start relying on executing tasks outside the chain that the chain itself cannot control, then 51% validators may collude to provide incorrect results, and users will lose their protection mechanisms.