Do people collect counterfeit money?

I am very new to collecting money. I saw a post earlier that was
talking about collecting counterfeit money I have a couple of
questions.

1) Do people actually collect counterfeit money? And I'm guessing this
is not legal (even though they are not trying to circulate it).

2) There was also comment about foreign counterfeit money not being
illegal here. Is that true as well... what about counterfeit british
money printed by the Germans in WWII?

Do other countries have as much of a counterfeiting problem as we do
in general?

Any comments welcome.