The Ethereum Virtual Machine (EVM) is what defines the rules for computing a new valid state from block to block. The EVM is a powerful, sandboxed virtual stack embedded within each full Ethereum node, responsible for executing contract bytecode. Contracts are typically written in higher level languages, like Solidity, then compiled to EVM bytecode.
This means that the machine code is completely isolated from the network, filesystem or any processes of the host computer. Every node in the Ethereum network runs an EVM instance which allows them to agree on executing the same instructions.