When I was a teen and made a malware for the Apple II : I could inoculate disks by putting the hex value $50 in an unused place of the VTOC that was stored on d

When I was a teen and made a malware for the Apple II : I could inoculate disks by putting the hex value $50 in an unused place of the VTOC that was stored on disk. $50 is P which stands for Parasite. This was before the word virus had taken hold and I called my program a parasite. I could prevent the parasite from infecting my and my friends DOS disks with this benign change.