If you're putting your Android phone or tablet up for sale on eBay, then a factory reset might not be enough to destroy all of the data on it. On some devices, the files and photos on your phone aren't actually erased—just the references and file structure around them. With a few hacking tools, anyone can scrape some of your data off. You can prevent that by taking one extra step before your factory reset: encrypt all the data on your device. This means even if someone else gets at your files after the factory reset, they won't be able to make sense of them. The encryption option is under Settings and Security on stock Android and will be in a similar location on the different variants of the OS.