I've just heard about this site, which people may find useful.
https://haveibeenpwned.com/Feed in a name, user name, email address, etc., it tells you if the password details etc. have been leaked. For example, my email address and login details turn out to have been leaked in the big Adobe hack a couple of years ago, which fortunately I already knew so I don't have to start panicking. And my details
don't seem to have been leaked in the hack of the NCIS fanfic archives a few months ago, but I've already taken steps about that one and it was high time I changed a few passwords anyway... It doesn't give you any details beyond saying there was a leak, so you can't e.g. feed in someone else's user name and get their password, although you could possible see a list of leaking sites they've used.
Well worth a look.