Fun Tandy story.
It was the 80s. My parent bought a Tandy 1000 SX for their business. It worked fine for a while, until one day it started randomly crashing, and occasionally showing a little dot bouncing around the screen.
They took that thing to countless computer stores to have it fixed. Nobody could figure it out. Everybody said it was working just fine.
My dad got so fed up he bought a new computer and told me that if I could fix it, I could keep it.
And of course I figured it out! Turns out, it was infected with the Ping Pong [1] virus. One of the very first viruses. Certainly the first I had ever witnessed, or anybody I knew for that matter. That day, John McAfee got me a free computer!