deleting recent documents

i am looking for program to help me delet the last document showing under the File tab
start word or excel then go to File at the bottom of the dropdown list there is a list of document names & locations of the last 4 doc i used. i wold lik to delet this list so no one can see what doc i used. preferable a program that run autometicaly like on shutdowen or startup. thank you