Open-sourcing is important to Hedera because it creates transparency in the Hedera network services codebase, hashgraph consensus algorithm, applications, development tools, and the engineers working day-to-day behind the scenes. Hedera believes that by having every aspect of its network open-sourced, we empower the community to become more involved in developing the network and its flourishing ecosystem. You can read more about the open sourcing of Hedera services in this blog posting and the open sourcing of hashgraph consensus under an Apache 2.0 license in this blog posting.
The hashgraph consensus platform code has been audited by multiple code audit firms. The audit from FP Complete for the hashgraph consensus platform code, as well as the COQ proof from Carnegie Melon, are made available on the 'Audits and Standards' page: https://hedera.com/audits-and-standards