Running a CTF / pranks

I'm designing, hosting, running a CTF for a few dozen high school students interested in cybersecurity. For the forensics series, they have to identify backdoors in systems, investigate how they work, and eventually it ends up with them having to join my IRC server pretending to be a bot in order to find some information I leak while controlling all of the systems in real-time as a red team. While they're busy investigating, I use the backdoors to do silly things like make a prompt appear saying "Hi anon, want to play a game?" or random flashing skull animations shoot across the screen, duplicating increasingly fast until the system crashes. Is there anything along these lines I might do for same challenges involving linux systems with only SSH access?

wall/write messages Trolling via aliases and or paths Trolling via hardlinks Changing PWD variable Sending back slightly corrupted or filtered text

>>19572 Oh soykaf, forgot about wall, that's a good one >Sending back slightly corrupted or filtered text Can you elaborate?

>>19572 if you have root then you can modify sshd or vt to corrupt text sent back to the player or filter it

You could have some fun with entries in their /etc/hosts. Have google point at a web server you're hosting and serve a rick roll video or something.

>>19573 look up zalgo text, lets you do soykaf like this

use find+alsamixer+aplay to locate sound files, boost volume, and play them I once found a bunch of farm animal noises, it was great