"We felt strongly about privacy when no one cared," Cook told an audience at Fortune's CEO Initiative event in San Francisco, California. "We could not see the specific details, but we could see that the building of the detailed profile on people likely would result in significant harm over time."
"It could be used for too many nefarious things," he added.
Cook's comments came in light of data and privacy making headlines in recent months, following data scandals and the roll-out of legislation in certain regions.
Earlier this year, Facebook said about 87 million users had their information improperly shared with a data analytics firm, which resulted in a massive scandal. In March, Cook criticized Facebook and said privacy was a human right and a core American value.
On Monday, Cook warned that people in today's environment do not have a full view of the kind of information others have on them. They don't realize, "how much of their lives have been opened to commercial entities and public entities," Cook said.