Please let me know how to check whether my iPhone 4s is jailbroken since I bought it from Germany on used from Amazon.
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How do I tell if my iOS device is jailbroken, and what can i do about?
If you can run unsigned code as root, then you're Jailbroken
The easiest way to check if an iPhone is jailbroken is to check for the Cydia installer/app. If you're on iOS 6 or below, just swipe all the way to the left to get to the search screen, and type in "Cydia." If you find that app, the phone is jailbroken. If you're on iOS 7, swipe down on your home screen to open the search box.
If you didn't find Cydia but still want to be sure it isn't jailbroken, check for other possible installer names, including "Icy," "Absinthe", or "Installer." If you don't find any of those, it's likely a stock iPhone.
One last telling point that an iPhone is jailbroken is the absence of default apps. If you see apps like Safari, Calendar, App Store, or Mail missing, the phone is jailbroken, as you cannot remove these apps normally.
Hopefully these tips help you find out the status of your phone!