This is probably something everyone should at least be thinking about when they go to sell or return old devices. I will add one thing, however. Earlier versions of some smartphones have been shown to leave behind some data even after being reset to factory settings. It would require a lot of work, and expertise, but don’t necessarily assume that everything is gone. In fact, I would treat my phone the same way the authors of this article treat computer hard drives. – Probably best to simply take out the one you used, and replace it with a brand new one if you’re getting rid of the machine. I wouldn’t turn over a functioning smartphone to anyone else if I had used it to store personal data.
“It occurred to us that probably thousands, perhaps millions, of consumer devices are returned to retailers around the world with consumer’s sensitive data. Those devices can take a multitude of forms – PCs, tablets, smartphones, video game consoles, and now even Smart TVs.
Consumers have sensitive data tied to various online services, including but not limited to Netflix, Hulu, PlayStation Network, Xbox Live, Amazon, Crunchyroll, Google Play, iTunes, and the App Store. These accounts often have credit card data tied to them, as well! But even if they don’t, letting an online account fall into someone else’s hands can have disastrous consequences. It may even result in identity theft or compromising a user’s entire online life.
So, here are some tips on how to keep your sensitive data on specific types of consumer devices from ending up in the hands of a third-party when selling, returning or giving away a device.”