Blockchain networks are maintained and secured through a combination of decentralization, cryptography, and consensus algorithms. Each participating node maintains a copy of the ledger, ensuring that transactions are visible to all. Miners validate transactions by solving complex cryptographic puzzles, and upon reaching consensus, new blocks are added to the chain. The immutability of the blockchain is further ensured through cryptographic hashing, making it difficult for any single entity to alter past transactions without consensus from the network, thereby enhancing security and trust.