[ivan4th]

I did write some DOS viruses back when I was a kid, including a "stealth" one (invisible when reading the infected files via int 21h) and another one polymorphic (encrypted with dynamically generated decoder). I've never spread them, although I did upload another simpler one to an antivirus vendor BBS as a "new virus", so now it's known as "Areopag-480" and such. I thought all of the sources of things I wrote back then were lost when I typed an extra space in "rm -rf ~/something" back around 2000, but recently, while looking through some old books, I've found a piece of code of the stealth virus I wrote around 1992-1993: https://twitter.com/ivan4th/status/1434625057553330178/photo... I didn't have a PC at my grandparents' dacha back then, so I was writing code on paper instead during the summer

[TigeriusKirk]

I did some of the same things back in the day, just because viruses seemed like such a neat idea. There was a book that came out, The Little Black Book Of Computer Viruses, that was very helpful in learning such things.

Text of the book here - https://web.archive.org/web/20090420151624/http://vx.netlux....