Mainnet is the live version of a blockchain network, where transactions are recorded on the network used by its participants. Unlike a testnet, its tokens and other assets may have real economic or operational value, and actions such as transfers or smart-contract deployments can have lasting consequences.
In cybersecurity, the distinction matters when software, wallets, or AI agents interact with blockchains. A testnet can support development, but its separate environment does not make every action authorized or harmless. Defenses include isolating test and mainnet credentials, limiting wallet balances and permissions, protecting signing keys from software agents, and requiring human approval for consequential mainnet transactions.