Spooked!

I've received an email fom an unknown hotmail address - which remains unopened - but the heading spooked me as it says 'Re: ...........'  which is scarily close to one of my secure passwords.  I wonder if the sender is hoping I will hotfoot it over to this site and put in the correct password to see if anything untoward is happening.  Is it possible that I could be tracked and how do you think someone has come up with this similar password?