Do this process for permanently delete the download files

Permanently deleated procedures:

For sale Smart phone factory reset is not only enough for erase all the data,its tell by many members but its not a truth.In this digital and electronics world once upload  a file permanently deleted is not possible its difficult,during the deletin some of the cache files are store in the separate folder.

This concept is same in the smart phone.after the click of reset button the downloaded files are kept in a folder.

actually many of the hackersprove thar factory reset deleted files are easily recovered some following steps.But dont get fear

Security:
before selling your mobile encrypt your files,today the latest android version 6.0 have this facility of encrypting the data.
In old mobile phones like kitkat and jelly bean following this route settings->security->encrypt phone options are clicked and do it
browsers & usage:
Many more security you need means after the factory reset and encryption processto save the much moredownloaded files are save,so the older important files can't recovered from any one.Its known as over write method.
Set up:
after the over writting process dont log in any websites or social network,take a long file video with the other camera application,now the memory card is filled and again factory reset,Now you get 100% security of your old files in your mobiles.