Thanks to the increase of virus across MS-DOS, Atari, Acorn, Amiga and Mac operating systems, specially on boot sector floppies, the general public learned that anti-virus were required software to always have installed.
Thus making anti-virus a software package, that most home users would buy, in my home country even that was usually pirated.
Probably only during the 8 bit computers it wasn't a problem.
If all you want is a DDoS, a fake advertising account can often deliver the desired effect without actually infecting anyone. It really depends on what the cost/benefit vs desired outcome is. Not everything requires root, and very few people actually check checksums for things they download.
The cracking scene was equally full of virus.
Only in the very early days, during the genesis of the demoscene, it was as you describe.