When returning a defective computer, simply deleting files or emptying the recycle bin does not ensure complete data removal, as Windows only marks the space as free without erasing the data. For secure deletion of sensitive files, tools like SDelete can overwrite the data multiple times, making recovery unlikely. A full disk format, rather than a quick format, is recommended for thorough data removal, as it writes over the entire drive. Physical destruction of the hard drive, such as drilling holes in the platters, is also an effective method but may void warranties if the computer is being returned. For those who have already emptied the recycle bin, using SDelete to clean free space can further obliterate any recoverable data. Programs like Recuva can help identify recoverable files from free space, allowing for targeted overwriting.