I already tried
- to find out my password by simply md5-hashing all my passwords I could think off and comparing them to the hash in
- to check whether someone could easily crack my password by putting the hash into some online md5 "rainbow table service" myself.
- to find the breached web site by searching my mail for registration notifications received on the registration date given in
- to find email received from any mail address in the list.
- to send an email to the first in the list, asking him whether he knows which site it is and/or whether he possibly is the owner of that site.
All of these loose ends came up blank.
I could only deduce that it has to be a really small LEGO-themed website, but that's it.
So I have changed all my passwords of my most-used accounts, especially the email accounts. The many old and sleeping accounts I don't know that I have, they are out of reach.
What else can I do?