Gas is the fee mechanism that pays for computation and storage changes on Ethereum. Every transaction that executes an operation, such as transferring tokens or deploying a smart contract, consumes gas. The sender pays the fee in ETH; the total cost depends on the gas used and the transaction’s gas price.
Gas matters for security because it limits resource use and makes on-chain actions costly. In attacks and operational mistakes, a compromised or overly permissive wallet can spend ETH on transactions an owner did not authorize, including contract deployments. Defenders should restrict which accounts an AI agent or application can access, keep balances limited, and require approval before signing or broadcasting transactions. Testnet gas, such as Sepolia ETH, is not ordinary mainnet money, but unauthorized use can still signal that controls over wallets and transaction authority are inadequate.