Factory reset button useless: Embarrassing selfies and personal data recovered on second-hand phones

It's probably something that most of us have done before. You want to sell your old Android phone, so you hit the trusty 'factory reset' button and away everything goes. Clean as a whistle, right?

Well apparently not, according to research from Avast Software, which showed just how insecure this can be by retrieving personal information from second-hand phones it bought on eBay.

Read more: "Worldwide security shift" needed for mobile security, says expert

The data retrieved included 40,000 stored photos, 750 emails, one completed loan application and four of the previous owners' identities.

Google issued a statement saying, "This research looks to be based on old devices and versions (pre-Android 3.0) and does not reflect the security protections in Android versions that are used by the vast majority of users."

It went on to offer some advice for potential sellers: "We recommend you enable encryption on your device and apply a factory reset beforehand; this has been available on Android for over three years."

Read more: Five tips for protecting your sensitive data

To do this, go into the security section of the settings menu and select 'encrypt device'. This will then mean that anyone who wants to access the data on the device will have to enter a password, so your personal information will be protected.

You can then go ahead and hit the 'factory reset' button to wipe the device and successfully return it to its original settings.