See "The Cuckoo's Egg" [1] by Cliff Stoll (who sometimes posts here [2]). A few related HN threads: [3] [4] [5]. The book describes tracking down a hacker in 1986 who exploited a vulnerability in early Emacs' movemail utility.

[1] https://en.wikipedia.org/wiki/The_Cuckoo%27s_Egg_(book)

[2] https://news.ycombinator.com/user?id=CliffStoll

[3] https://news.ycombinator.com/item?id=21830277

[4] https://news.ycombinator.com/item?id=39843930

[5] https://news.ycombinator.com/item?id=49406713