I work for a small MSP, and we have a client that runs a large wholesale bakery and distribution center. Most of their office staff is in a clean, air-conditioned wing, but they have one "shipping and receiving" terminal located right on the edge of the warehouse floor where they handle bulk flour and sugar.

I get a high-priority ticket: "PC is compromised. Loud siren noises coming from the tower, mouse is jumping everywhere, and Excel takes 5 minutes to open. User is convinced it’s a massive malware infection."

I drive out there, expecting maybe a dying HDD or some actual nasty software. As soon as I walk into the shipping office, I hear the "siren." It’s not a software alert; it’s the CPU fan spinning at maximum RPM, sounding like a miniature jet engine trying to achieve takeoff. The user is sitting there, looking terrified, hands off the keyboard.

"It’s been doing this since 10 AM," he says. "I think some script is running in the background and eating all the resources. Look at the lag!"

I open the Task Manager. CPU is at 100% load, but the clock speed is throttled down to about 0.8 GHz. The poor i5 is basically gasping for air. I peek at the back of the case and the intake vents are completely carpeted in a fine, white, sticky felt.

I take the side panel off and a literal cloud of flour and dust hits me. The heatsink wasn't even visible; it was just a solid block of organic "felt" baked onto the fins by months of heat. The fan was trying its best, but it was just circulating hot dust.

Me: "It’s not malware. It’s the flour."

User: "What? No, I ran a scan last week and it was clean!"

Me: "Your CPU is literally cooking itself. This isn't a digital attack, it's a physical one."

I took it outside, hit it with a dedicated data vac, and watched a white mushroom cloud erupt from the case. Five minutes of cleaning, a quick repaste because the old stuff was crustier than a week-old baguette, and suddenly the "virus" was gone and Excel was snappy again.

I told the manager they need a sealed industrial case for that area, but they’ll probably just wait until the next "possession" in six months.

TL;DR: User thought a high-level virus was screaming through his motherboard. It was just a clogged fan and a CPU hitting 100°C because of warehouse flour.