Re: "Try finding a virus that would both be capable of infecting a PDP-11"
I remember a conversation by email with my brother from ... oh ... at least 15 years ago now ... concerning his job writing an emulator to allow PDP-11 code to run on PCs of some sort.
And I, too, wrote PDP-11 code back in the day. In assembler, too. Uni course with the final project organised as a competition to see which of the four groups could get the best aggregate score for a sort of jigsaw-solving algorithm(1). The score was an aggregate based on memory used and time taken.
My group won the competition with the best time *and* the smallest program. Two other groups were close behind, while the fourth trailed far, far behind because they wrote a chunk of the code in Pascal, producing a result that used prodigious amounts of CPU time *and* memory.
(1) N by M puzzle, each piece was four integers to represent the four edges of the piece. A zero meant an edge piece, while a pair of zeros meant a corner. Two pieces were correctly adjacent if there was a particular arithmetic relationship between the numbers. The pieces were all aligned correctly (no rotation was needed), but arranged in no particular order.