I can't speak for the specificity of parent's "evil maids" phrase but the concept of an "Evil maid" is used in security scenarios.
A maid tends to be an example of a person who's mostly a stranger, but is given unmonitored access to your most private spaces for prolonged periods of time. So they theoretically become a good vector for a malicious actor to say "hey I'll give you $$ if you just plug in this USB drive in his bedroom laptop next time you're cleaning his house" - it's often used in the scenario of "ok what if someone has physical access to your resource for a prolonged period of time without you noticing? what are your protections there?"
alt Hacker News
I can't speak for the specificity of parent's "evil maids" phrase but the concept of an "Evil maid" is used in security scenarios.
A maid tends to be an example of a person who's mostly a stranger, but is given unmonitored access to your most private spaces for prolonged periods of time. So they theoretically become a good vector for a malicious actor to say "hey I'll give you $$ if you just plug in this USB drive in his bedroom laptop next time you're cleaning his house" - it's often used in the scenario of "ok what if someone has physical access to your resource for a prolonged period of time without you noticing? what are your protections there?"
I wonder if that's what OP meant? :-)