Re:An opinionated history of programming languages
by Rochus on Monday October 05, 2020 @04:07AM
(#24685596)
Classes and "virtual" procedures were indeed already part of the original "Simula 67 Common Base Definition" in June 1967, but "protected" and "hidden" were added later (proposed here https://dl.acm.org/doi/abs/10.1145/956003.956009, and probably added to the Common Base Language in 1982).
Every time you write "protected" or "virtual", that's Simula speaking.