Bitcoin Core is free and open-source software that serves as a bitcoin node and provides a bitcoin wallet which fully verifies payments. It is considered to be bitcoin's reference implementation. Initially, the software was published by Satoshi Nakamoto under the name "Bitcoin", and later renamed to "Bitcoin Core" to distinguish it from the network. It is also known as the Satoshi client. Bitcoin Core includes a transaction verification engine and connects to the bitcoin network as a full node. As of 2013, peer-reviewed measurements of the Bitcoin network's message propagation showed that new blocks reach 95% of nodes within about 40 seconds and a median delay of 12.6 seconds, underscoring the importance of efficient node software such as Bitcoin Core.