Do not sell your Android phone! Has your saved data – FORTUNE

(CNNMoney) – Are you going to sell your Android phone? Do not. You have your stored data.

If you recently sold your old Android phone, it is likely that your text messages, your emails, your photos and your key Facebook follow him even if you cleared the memory.

Researchers at Cambridge University did a study that reveals that the “factory settings” option, at least on Android devices, does not erase everything. Moreover, sometimes even erase much.

The market for smartphone used is huge and there are about 630 million users susceptible to this problem, according to the study. Wall Street analysts believe the market will continue to grow at least until 2018.

The researchers tested 21 phones with Google’s operating system: HTC, LG, Motorola and Samsung devices. In all cases, they could retrieve text messages, identification data of Google accounts and conversations messaging applications. 80% of the time a few emails were stored in the device.

In addition, the tokens special applications that let you access your account from Facebook and other social networking accounts were stored on the device.

Sometimes the devices are not properly cleared the special part of the memory of your phone where all your photos and videos are stored.

Among the affected devices are the HTC One; HTC Sensation; Motorola Razr; the Galaxy S, Galaxy S2 and Samsung Galaxy S Plus, and more.

The researchers said that the Nexus 4 of Google was the top performer, but it was not without problems.

Each phone showed a different variety of problems. For example, the HTC One did not erase the internal SD memory (where the photos are stored) through the “settings” menu of the phone but that’s what HTC tells you to do. To do this, you have to go through the menu “recovery mode.”

Part of the blame lies with Google, which is what makes the software Android with all these phones work. But also to blame manufacturers of mobile for bad design, improvements and upgrades software terribly behind, according to the researchers.

If you’re serious about selling your old phone, no way to be sure that your data is completely erased.

Delete manually each photo, message and application does not work either. Select the “delete” option does not really destroy that file on your phone because memory flash (which use mobile) is notoriously difficult to erase.

Another technique might be password-encrypt everything on your phone. But then you can not sell your phone.

“This may be hopelessly complicated,” said Ross Anderson, a professor of engineering at Cambridge, who helped lead the study.

Per Thorsheim, a security expert from Norway, offered a different and more brutal approach.

“Do not give your phone. Destroy it,” he advised.

Google did not respond to questions put to him for this article. The company usually encouraged to try several things: to wipe away the phone as if he had stolen; select the “factory settings” option and upgrade to a newer version of Android to enable password encryption.

But researchers say that’s not 100% reliable.

Fortunately, Google offers an option to protect your information related to Google (like Gmail, Drive documents and maps). You can open Gmail, go to control panel Google and “revoke” access that device to your Google account.