@rocketsoup Searched 'Klein bottle'. Another useless knowledge item to clutter my diminishing brain. Best part about the search is that a company named Acme makes glass Klein bottles.
@LovingFalloutLondon1954 @rocketsoup It's Cliff Stoll! He's an astronomer and in 1986 when working as a system admin he uncovered a KGB hacker. See also this video where he shows off his operation: https://www.youtube.com/watch?v=-k3mVnRlQLU
The man with 1,000 Klein Bottles UNDER his house - Numberphile

YouTube
@bloody_albatross
Didn't know the thing about the KGB hacker. Do you recommend any article or video I could read/watch to learn more about this? If not I'll just take the first hit on <search engine>, works as well.
@LovingFalloutLondon1954 @rocketsoup
@cafeinux @LovingFalloutLondon1954 @rocketsoup I don't remember where I heard about it, probably some YouTube video. People say his book about it (The Cuckoo's Egg) is a good read. Haven't read it myself.