Avast, which makes security software for Windows, Mac, and Android, recently bought 20 used Android handsets on eBay. Then company employees used digital analysis software that's readily available and fairly easy to use to see if there was anything left on the 20 devices from the original owners. It turns out there was. Avast researchers found more than 40,000 photos, 750 emails or text messages, and 250 contacts. The group was also able to deduce the identities of the previous owners of four of the phones.

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It's important to note that Avast makes its own reset software, which the company claims does a much better job of completely wiping Android devices. So part of the motivation for this study is presumably to promote Avast's alternative service. Still, the results are pretty startling. Whether they make you want to buy Avast's software or someone else's, this test at least raises awareness of how hard it is to scrub personal data before reselling or donating old devices.