What Is a 51% Attack?
A 51% attack occurs when a single party gains control of the majority of a blockchain's mining power (proof of work) or staked capital (proof of stake). With that majority, the attacker can decide which version of recent history the network accepts — allowing them to reverse their own recent transactions and spend the same coins twice.
The classic move: deposit coins on an exchange, withdraw something else, then use majority power to rewrite the chain so the original deposit never happened. The attacker keeps both sides of the trade.
What an Attacker Can — and Can't — Do
Can: reorganize recent blocks, double-spend their own coins, and censor or delay other people's transactions while in control.
Can't: steal funds from other addresses (that still requires each owner's private key), create coins out of nothing, or change the protocol's rules — every node still rejects invalid transactions.
Why Large Networks Resist It
Majority control of a major network requires enormous, sustained real-world cost — hardware and energy, or a majority of all staked capital.
A successful attack undermines the asset the attacker holds and mined or staked to obtain, destroying their own investment.
Proof-of-stake networks can additionally slash an attacker's stake, making the attempt directly self-destructive.
Small networks with cheap, rentable hash power are the realistic targets — one reason exchanges require more confirmations on them.
51% Attacks and Trust Wallet
No wallet can change a network's consensus, but self-custody keeps the part you control secure: with Trust Wallet, your keys stay on your device, so no chain-level event can sign transactions on your behalf. For extra caution on smaller networks, wait for more confirmations before treating a large incoming payment as final.
