# Zebra checkpoints
Zebra validates [settled network upgrades](https://zips.z.cash/protocol/protocol.pdf#blockchain) using a list of `Mainnet` and `Testnet` block hash checkpoints:
- [Mainnet checkpoints](https://github.com/ZcashFoundation/zebra/blob/main/zebra-chain/src/parameters/checkpoint/main-checkpoints.txt)
- [Testnet checkpoints](https://github.com/ZcashFoundation/zebra/blob/main/zebra-chain/src/parameters/checkpoint/test-checkpoints.txt)
Using these checkpoints increases Zebra's security against some attacks.
## Update checkpoints
Checkpoint lists are distributed with Zebra, maintainers should update them about every few months to get newer hashes. Here are [the exact commands for updating the lists](https://github.com/ZcashFoundation/zebra/tree/main/zebra-utils/README.md#zebra-checkpoints).