A very simple concept worm written in MS-Batch (designed for Windows 10 21H1, should work on Windows 11)
A payload could easily be added, though I created this just for testing some stuff, and as such have not included one. It also wouldn't be very good for that, as it's easy to detect and really only spreads using network drives.
Any payloads added and/or consequences that come from it are your own fault, I made this just for security testing — it's not meant to be used to cause harm.