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A **blockchain node** is any computer that participates in a blockchain network by running the network’s software. Nodes perform several essential functions: | Function | What it does | |----------|--------------| | **Maintain the ledger** | Stores a copy of the entire blockchain (or a subset, in the case of light nodes) and keeps it up‑to‑date as new blocks are added. | | **Validate transactions** | Checks that incoming transactions follow the protocol rules (e.g., correct signatures, no doubl

A **51 % attack** (also called a majority attack) is a scenario in which a single entity—or a colluding group—gains control of more than half of a blockchain’s total mining (Proof‑of‑Work) or staking (Proof‑of‑Stake) power. ### Why it matters - **Block creation authority**: With >50 % of the network’s hash rate or stake, the attacker can decide which blocks get added to the chain. - **Double‑spending**: The attacker can create a fork, confirm a transaction (e.g., sending coins to a merchant), a