Teensy 2.0 project to reset wallpaper when coworkers leave their Windows machines unlocked.
This uses the Teensy's USB disk mode where leftover flash storage is available as a read-only drive. The keyboard emulation opens a command prompt and types in a batch script to locate and execute the payload from the drive.
This is an old project I'm sharing for fun, out of date and unmaintained, yadda yadda.
Add your desired wallpaper as bieber.jpg in disk/. On a Teensy 2.0 with 31.5K of Flash, I had about 8KB of space left for the image. I used a heavily compressed low-res (240x180) image in tile mode both to make it fit and to make it extra-hideous.
Build Pwn.ino with the standard Arduino+Teensy tools with the Teensy's USB mode set to Keyboard+Disk (pointed to the disk/ folder).
After plugging in the Teensy, it waits 30 seconds for Windows to figure out drivers, then starts typing. The LED lights up during the last 3 seconds of the waiting period to warn that things are about to start happening.