In order to securely delete files, users have to understand the specific methods of an operating system and how to get access to the raw data where it resides on a machine. While many modern operating systems make it easy to disconnect access to digital files, they don’t actually destroy the information, and without specific security techniques, others could reconstitute that information later.
In order to actually delete files in a secure way, users of systems running operating systems like Microsoft Windows and other modern options often have to access the actual data and rewrite it so that it cannot be recovered. For example, the Microsoft Windows "Send to the Recycle Bin" option appears to delete a file, because it deletes pointers to where that file is stored. In order to permanently delete it, experts suggest using specialized software tools that go in and rewrite all of the binary data on the drive with a random combination of ones and zeros.
The secure and permanent deletion of files has become a big issue, partly because of rules around the disposal and recycling of old pieces of hardware. That, combined with the quick obsolescence of devices, makes it very important to many users that they control the information they have stored on a device before they release it from their possession. Stray data can be used for identity theft and other kinds of fraud.
Another alternative for securing information is encryption, where instead of deleting everything, users can take advantage of an easy encryption key to prevent others from misusing their personal data. Encryption can be much more efficient than rewriting an entire drive, and while the data may still be resident, it will be resistant to unauthorized access.