Is factory reset a re-image or just a delete and resetting of flags?

[AC Question]

My samsung galaxy 3 tablet was hacked. Screen flickered, screen went blank, then it started the Root process. This occurred when I clicked on a music video on U-tube. I immediately turned off internet connection and did the factory reset. Need to know if tablet is now safe to re-use or will my tablet never be trust worthy again? Does the factory reset re-image back to the beginning and clear out any nasties that a hacker would have buried deep or just delete files/apps and flip flags?

 

[Rukbat]

A factory reset deletes anything you've added since it came out of the box. It doesn't add things it had when it was new that you deleted. So it's not a re-image, but it doesn't delete everything.