An AT command is a text-based control instruction sent to a modem or cellular module to change behavior or query status. The name comes from the old "attention" prefix, and the format is still widely used to configure radios, read signal information, manage calls, and inspect network state.
In cyber security, AT commands matter because they are a privileged control plane for the baseband or modem subsystem. If an attacker can inject or redirect AT commands, they may alter connectivity, read device information, or trigger unsafe modem actions. In some cellular devices, SIM toolkit features can reach command-handling paths, so defenders must treat modem interfaces as sensitive inputs. Protection includes limiting who can send AT commands, validating command sources, disabling unnecessary command features, and testing modem firmware for unexpected command exposure.