So I just got into NameCoins b/c my mining pool is now also issuing those.  I went to register at a namecoin exchange and got an error that my email was already in use.  Weird, i thought, but I guess I could have set up an account without remembering it.  I went to retrieve my password and logged into the account without problem (it was a password reset so I have no idea if it's one of my typical passwords or not).  Funny thing is that once I logged in, there were BTC there and NMC and all sorts of other currency there that I have no recollection of putting there.  We're talking a pretty big amount, even if it was from a decade ago when I dabbled in BTC and then forgot about it, there is no way I had that many.  We're off by a few orders of magnitude.

I figured that they were accidentally transmitted to a wrong address or something, but since BTC is untraceable, how do I return this money?

There is one more possibility, which is someone used my email address to signup for an account.  The email I use for this account is something very generic, like bob@yahoo.com (not actually it, but as an example).  Could this actually be an active account that someone is using with a fake email address?

What do I do here?