Someone just attempted to enter my condo unit. This person had a ring of keys. She unlocked and opened my door. She did not knock. She was not wearing a security guard uniform and was not accompanied by security. I did not receive any notice from the condo that anyone would be entering my unit. She claimed it was a "mistake" when confronted. What is my recourse here? I don't know if this person was acting on behalf of the condo. If she was, it was a gross violation of privacy (no notice.. not even knocking!). If she was not, that's even worse that someone would have the key to my condo! I am planning to change the lock by calling a locksmith service so that I don't have to worry about this all the time.

That is awful news. I suggest you replace those locks ASAP. If you are in the Toronto area, I suggest using UTS Group.