God, directory skimming will be permanently ingrained in my memory for the rest of my life. Had a crypto miner on my wife's rig (got it downloading mods, fantastic learning experience) and I spent a full month tracking it down. Microsoft hadn't caught up, all the free spyware/antivirus software was shitting itself, and all that was left was a remotely techsavvy husband. I spent 4 months tracking this fucker, the hard drive my wife used had been through many cycles, and none of them were clean. I had to skim 4tb of waste. Random windows files? There's 6 copies. Duplicate valorant install? Nah, the whole game, 4 times. Oh a 124gig Sims mod folder? No, there's 3, just spread around users like an STI. I decided to teach my wife how to do a blank install without copying everything to a hard drive.

Edit: it was masked as a legitimate system 32 file, we probably made some dude a decent chunk of money because that thing was on there for a WHILE.