What is the name of that series where people were marooned on an island and somebody was sneaking around filming them?

The series you're referring to is likely "Survivor." In this reality competition show, contestants are marooned on an island and must outwit, outplay, and outlast each other to win a cash prize. While there are no hidden cameras in the traditional sense, the production team films the contestants as they navigate challenges and social dynamics in isolation.