It’s been a while so I don’t remember. I was like 8 or 9 years old.
I’m assuming someone somewhere told me about viruses and gave me a copy of McAfee.
I remember when it all clicked though. All our computers started acting the same with the ping pong ball. The virus was spreading whenever I was inserting a floppy in an infected machine. I had a ton of floppies to clean.
Download the shareware version of McAfee ViruScan from a BBS, I imagine, and then maybe buy a virus cleaner? Or, more likely, make an illegal copy of one.