Holy Blast from the Apple Past! The virus you have in the Youtube video looks similar to Killer DOS that I had seen in the 80's in the way that it would infect disks, however, the one in your video is much much less amazing than the true Killer DOS that I witnessed during the same timeframe.
The Killer DOS that I witnessed had an amazing kill screen. It blanked out the screen and had white borders everywhere with flashing inversed text space bars and it said "You are a victim of Killer DOS!!! Everything on this disk has been degaussed!" directly in the center of the screen and it was flashing text.
But the most amazing thing about it was as the kill screen was being displayed, it played the most eeriest and freakiest sound that the Apple IIe was capable of at the time. It was so good, I have digitized it and I may be able to dig it up. Also, at one point in time, I was so fascinated in the sound from the kill screen that I was able to export just the sound routine in assembly language and I could run the sound routine in DOS.
Some other things I remember about it. As the other person mentioned on the Apple site 20 years ago, it did come on a speech synthesized disk containing several other programs and it said "You have chosen Killer DOS Editor" when you selected the Editor. Killer DOS Editor was created or partly created by or distributed by Die Katze (German for The Cat). From what I remember, the editor allowed you to change the number of DOS commands that needed to be issued before the kill screen would commence. But it was so long ago I don't remember all the details of the editor. I believe it also let you infect a disk that was not previously infected.
Now it could have been the exact same version of Killer DOS and maybe somebody just figured out how to add the amazing kill screen and sound routine to it. Either way, it was pretty amazing and it's unfortunate that you were not able to see the full kill screen in all its glory. You would have been amazed. Anyway, does anyone here remember a user named Die Katze by any chance? That person would be able to fill in many more details about this lost piece of software. Also, has anyone else besides myself seen the version of Killer DOS that I am referring to with the amazing kill screen and sound?
Apple II DOS Master, does what I have described sound like your version of Killer DOS, or was yours different? I seem to remember a reference to The Master and The Wizard but I don't recall 100% if it was from the kill screen or from Apple Warez of the time.