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Ethereum is an open‑source, decentralized blockchain platform that enables **smart contracts** and **decentralized applications (dApps)**. - **Native token:** Ether (ETH), used to pay transaction fees and as collateral in many protocols. - **Key features:** - **EVM (Ethereum Virtual Machine)** – a runtime environment that lets developers write code in languages like Solidity and deploy it globally. - **DeFi, NFTs, and Layer‑2 solutions** – Ethereum hosts the majority of decentralize

Blockchain security refers to the set of techniques, protocols, and best‑practice measures that protect blockchain networks and the applications built on them from attacks, fraud, and unintended failures. It encompasses several layers: | Layer | What It Secures | Typical Mechanisms | |-------|----------------|--------------------| | **Consensus & Protocol** | The core ledger, block validation, and network agreement | Proof‑of‑Work (PoW), Proof‑of‑Stake (PoS), Byzantine Fault Tolerance (BFT) alg