Hello carolseptember,
An image of this would be nice! Your Mac does not need anti virus, desktop cleaner, etc. software. Your MacBook has some pretty strong features to protect you and your data. Usually anything claiming to do this is spam / malicious software in of itself.
The best thing to do is force quit out of the app you believe is causing it.
A little more advance, but Activity Monitor can be used to track unknown and unwanted applications - Activity Monitor User Guide for Mac - Apple Support. It is advised to go through this. The Network tab is usually the most interesting. Kill any process you do not recognize.
Go through the sections of Privacy & Security within the Settings app and revoke access to apps that shouldn't have certain permissions. I would be careful with:
- Files and Folders
- Microphone
- Screen Recording
- Camera
- Full Disk Access
- Location
I would suggest looking at Privacy & Security within the Settings app and going through Safety Check. Revoke access to people and apps that are utilizing privileges you believe they shouldn't have. Changing your Apple ID password and device passcodes might also be smart.
If you did download the legitimate Norton software, although you don't need it, they should have a remediate button within their app (I assume).
To prevent future incidents:
- Do not interact with unknown senders.
- Do not click on unknown links or attachments.
- Do not travel to sketchy and unknown websites.