Various embodiments herein each include at least one of systems, methods, and software for computer pre-boot security verification. Some embodiments are implemented during a boot sequence of a computer that controls Self-Service Terminal (SST) operation before a main Operating System (OS) of the computer is loaded. One such embodiment in the form of a method includes starting a pre-boot OS upon start of a computer that controls operation of an SST and identifying any variances between a current state of the computer and data representative of a reference state within a computing environment of the pre-boot OS. This example method further includes performing at least one remedial action when any variance is identified and launching a main OS and stopping and unloading the pre-boot OS when no variance is identified.