Smartphone security: questions about Androids

New research is raising some questions about data security on Android phones.

Researchers at the University of Cambridge say the "factory reset" on Android devices doesn't actually erase everything in your phone. These findings could make you think twice about selling your used Androids in the future.

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In fact, one expert offered a rather startling suggestion about what to do with your used phone. More on that in a minute.

First, CNN Money reports researchers tested 21 phones made by Google, HTC, LG, Motorola and Samsung. In every case, they were able to recover text messages, Google account credentials, and conversations on messaging apps. A few emails remained on the device in 80 percent of the cases.

Researches say the Google Nexus 4 performed the best, but it still had issues.

Can You Truly Delete Your Data?

If you are looking to get rid of a used phone, can you truly delete your data? CNN Money says manually deleting every photo, message, and app doesn't actually work because flash memory, used by these phones, is very difficult to erase.

One cybersecurity expert from Norma offered a brutal approach to this data issue. He told CNN Money, you'd be better off smashing your old phone, rather than giving it to someone else.

Google didn't comment for this story. There is a way to protect your Google-related stuff, such as Gmail, Drive documents, and maps) You can open Gmail, head to Google dashboard and "revoke" your phone's access to your Google Account.