Abstract: A hardware serial adapter that can be connected to a serial port of a physical computing device and is associated with network credentials that include a unique hardware identifier and other security information. Upon receipt of data (or other initiation command), the hardware serial adapter transmits a registration request with the network credentials to a distributed network service. If the network credentials are valid, the network service provides communication channel configuration information and session credentials to establish a secure communication for the transmission of data from the hardware serial adapter to a virtual machine instance. The distributed network service can control and manage data transmissions and the communication channel.