Android's factory reset function isn't as effective as we'd all like it to be, according to a team of Cambridge University researchers. The group estimates that as many as 500 to 630 million Android devices might not be capable of completely wiping the data saved in their internal disks and SD cards. They came to that conclusion after testing 21 devices running Android 2.3 to 4.3 from five different manufacturers that already went through factory reset. During their tests, they were able to recover at least part of the data stored in each sample device -- even if it was protected with full-disk encryption.