I have had this happen to me at multiple forums.
Someone registering my nickname and even my email 
address with it. Either obsessive nature or a 
prankster.
This happened to me like twice. Needless to say I 
wasn't happy, but who cares. Also, it could be 
someone trying to crack a password, I doubt they 
would do it that way though. Most cracking 
individuals use Access Diver III. It basically 
searches through a list of words and shows 
available words that match up to passwords.
Which are accounts that end up on another page of 
the program.

IE: "Cat", if you use that for a password then 
your pretty much screwed as this utility searches 
through literally thousands of words depening on 
how you configure it. (IE: make a word pad thats 
readable and add words like a lunatic)

I have experience with such things, and let me 
tell you its not very hard. Whilst other stuff 
can take days and days of work.
Almost all normal words used as passes can be 
cracked. EASILY in fact. 

My advice would be to learn the things people use 
yourself. One way or another no matter what you 
do, your IP can be seen. Unless you have a ghost 
connection. Then again I think there is also a 
way around that. 

Gibberish is your best bet password wise.
IE: "HDIHGF428F67YFYg87RyfihG"

Thats not a normal word and wont match up to 
anything (safe), crackers read the available 
stuff backwords, forwards, scrambled, etc.
I would have done the same thing EBAY wise.