Once upon a time the physics department terminated my computer and relegated me to a noisy room with a desk and a PC equipped with only one wordprocessor (ChiWriter, an abomination).
I was able to secure the PC with a few commands in the autoexec.bat file
The first two insured that onlookers were not shown what was going on, the last one parked the hard drive and halted the processor (the latter act was non-standard). I would switch on the computer and terminate the batch job with <CTRL-C>, and run a different batch file to start the word processor. The rest of the department thought the box was broken, since <CTRL-ALT-DEL> would not reboot it. (security by obscurity was effective in this case)