You have 1 TB, if you format and rewrite then your driver will have the new data. No one can extract the previous data.But if you fill your driver and then format it,without rewriting data , the data are not deleted. they are just marked as deleted . So when you give your drive to the other person, with some programs, he can find what data was writen in that place of the driver
RE: Even if you delete or format your disk , someone can find your data!