Okay, so "back up my data" is not only a good idea, Android also makes it really easy. People love good and easy. Google keeps all your data safe and encrypted, so even if you drown your phone or accidentally delete that picture of you and your bestie in the Tower of London, it only takes a visit to the cloud to recover. This back up feature is turned on by default in every Android device. You could turn it off but people don't.
But here's the thing: it's not just your data being backed up. It's all the data you require, which is a little bit different. Take the Wi-Fi password you use at your local coffee shop (mine is "blueberry"). That's not your data--you couldn't change it, for instance. But you have it. And along with all your pix and email, you send that along to Google too. What does that mean? Statistically it means there's a good chance Google has the passwords to almost every Wi-Fi setup in the world. Because Android, despite Apple's branding victories, is the clear worldwide leader in smartphone operating systems. So it's very likely that an Android device has logged into an existing Wi-Fi network, and it's pretty likely that one of those devices backed up the info at Google. Does Google want the info? No, it's just offering you a service. Does it mean that the NSA or other government groups have access to the login information of nearly every Wi-Fi network in the country? It might.
Extra: Security Expert Michael Horowitz goes into detail here. And so does John Leyden at The Register in the UK, and information technology site which has the exquisite tagline, "Biting the hand that feeds IT".
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