Shtyle.fm Sent spam using my name without my knowledge or permission, Internet

Shtyle showed me that I was not nearly as Internet sophisticated as I thought.  I received an invitation from a friend to join Shtyle.  I accepted, and was prompted for, among other things, my e-mail password.  I unthinkingly complied (what was I thinking?), and within a few minutes I received e-mail from someone saying they had accepted my invitation to become a 'friend' on Shtyle.  I, of course, had not knowingly invited her.  Shtyle had apparently gotten her e-mail address using my password.