Normal user when they want to delete their files, they will drag their files to Trash and select Empty Trash. But, after you empty the Trash, deleted files can be recovered using data-recovery software. Empty Trash just free the space that occupies by your deleted data and let the Mac OS X to use the free space to write the new files or data.

To delete files so that they cannot be recovered, choose Finder > Secure Empty Trash (more…)

By default, Mac OS X hire all files extension. If you want to show file extensions, just choose to show extensions for all files.

First, select Preferences from your Finder menu or used the keyboard shortcut <command> + <,> to open Finder Preferences window.

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