Getting random pop up screen with request to authorize changes on my Mac that I didn't initiate

I think I might have gotten hacked. I mistakenly opened a link sent to me in FB messenger by one of my friends. Turned out she was hacked. Now I think I might have some kind of malware or spyware because my computer has been acting weird since then. Random screens will pop up from time to time with a request to authorize changes and asks for me to enter my password. Also I noticed that while I am on my computer, a sudden screenshot will take place that I did not initiate. It has happened a few times now. Could someone please tell me what I need to do to stop this and prevent any further invasion of my privacy. I get the sense that someone else is seeing my screen from a remote location. Thanks so much