In my activity summary on programmers I have an entry
- 5 User was removed
What does this mean? Which user was removed and how is my user account related to this?
A user who had voted on one of your posts had their account deleted, either by choice or because they violated the Terms of Service. When that happens, the user's votes go away as well. -5 means that you had earned +5 points from them, probably via a question upvote, and unfortunately that reputation no longer exists.
As for which account was removed, that's not something we should share in public, sorry.