Robert Graham has posted a web form that converts your password to an SHA-1 password for lookup and provides a link to the file of LinkedIn passwords that were dumped on the Internet so you can download and see if yours is in there.
His was, mine was and I’d guess chances are good yours, Bill Lumberg’s and Nina from Corporate Accounts Payable’s are, too. The raw file is over 270 MB (120 MB zipped) so don’t open it in Word unless you like the spinning rainbow wheel a lot.
If you haven’t already, you should change your LinkedIn password and email login, certainly before you use this tool.
Update: Glenn Fleishman notes you can achieve the same lookup by typing the following into the Terminal which doesn’t require you to send your password over the airwaves.
echo -n ‘plain-text password’ | openssl sha1
Mine was unique to LinkedIn and I had already changed it so it wouldn’t be an issue if it had been compromised. Well, further compromised, I guess.