# 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](./main-checkpoints.txt)
- [Testnet checkpoints](./test-checkpoints.txt)
Using these checkpoints increases Zebra's security against some attacks.
## Update checkpoints
Checkpoint lists are distributed with Zakura, maintainers should update them about every few months to get newer hashes. Here are [the exact commands for updating the lists](../../../../zakura-utils/README.md#zakura-checkpoints).