You think a stranger (say computer repair guy) might have had access to a computer file with your SSN in it over the past few days. You don't know if person has seen the file or not, but you don't trust them too much. What's the best course of action to be taken so that identity theft and any other future problem is prevented?
EDIT: Suppose you also strongly suspect the "Computer Repair guy" is not an upstanding person and you know for a fact he has been involved in criminal activity in the past