I once stayed late and noticed a cleaner was wearing a polo from the company I used to work for. I asked him about it and it turned out he was an engineer and was filling in for his girlfriend who owned the cleaning business. Holy red flag! I made some noise and that cleaning company was let go.
Pro-tip for anyone that finds themselves in this situation when trying to steal another company's data - say you bought the shirt for 50c at a second hand store. That, or don't wear your company polo on an espionage mission.
He was working for the cleaning business, though. If the company was letting in anyone who works for that cleaner without further investigation, that's their problem. That's the situation we were talking about upthread, so I assumed
zcrackerz would have said something if it were different.
Where I work, each cleaner gets a badge, just like the engineers. Presumably she gave her badge to a random other person, aka her boyfriend, so he could let himself in. Nothing stops me from doing that as an engineer either, but it would absolutely be a firing offence if caught.