What Is a 51% Attack, and Why Is DigiByte Harder to Attack?

A 51% attack happens when a single miner or coordinated pool gains majority control of a blockchain's hashing power for a specific algorithm or network. With that majority, an attacker can mine a private chain in secret, then release it once it is longer than the public chain, causing other nodes to reorganize onto it. That reorg can let the attacker double-spend coins they already spent publicly, or temporarily prevent other users' transactions from confirming. It does not let an attacker steal coins from wallets they do not control or change the fixed supply, since those protections live in cryptographic signatures and consensus rules the attacker cannot forge.

DigiByte's MultiShield design raises the cost of this attack substantially compared with a single-algorithm chain. Instead of one proof-of-work algorithm securing every block, DigiByte splits mining across five independent algorithms, SHA256d, Scrypt, Skein, Qubit, and Odocrypt, each targeting roughly 20% of blocks, with difficulty retargeting independently per algorithm. To force a sustained reorg, an attacker cannot simply buy majority hashrate on the most accessible algorithm; they would need to dominate enough of the block production across the relevant algorithms while MultiShield actively rebalances difficulty in response, which continuously erodes any temporary advantage.

This does not make DigiByte immune to a 51% attack, since no proof-of-work chain is mathematically impossible to attack, but it does make coordinating and sustaining one significantly harder and more costly than on a chain secured by a single algorithm, because the attacker's leverage is fragmented across five separate hashrate markets instead of concentrated in one.