By jailbreaking your Apple TV 3, you can modify your device and install unique themes through third-party apps from outside of Apple's built-in App Store. For now, Apple TV 3 can only be jailbroken using a software called Snow3rd on Windows computers.
Step
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Step 1. Make sure your Apple TV 3 is running iOS 5.0.2 or earlier
Snow3rd cannot jailbreak Apple TV running iOS version above 5.0.2.
Go to “Settings” > “General” > “About” menu to find out which iOS version is installed on your Apple TV 3
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Step 2. Make sure you can access or use a computer running Windows 7, Windows Vista, or Windows XP operating system
Snow3rd is only compatible with those older versions of Windows, and is not compatible with Windows 8 or Mac OS X.
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Step 3. Visit the Snow3rd website at https://snow3rd.com/ and click the “Snow3rd Download” link
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Step 4. Select the option to save the.zip file to the computer desktop
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Step 5. Close all applications and end all running processes on Windows computer
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Step 6. Connect Apple TV 3 to the computer using a micro USB cable
The Apple TV USB port is on the back of the device.
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Step 7. Disconnect the Apple TV from the power source/wall socket
The only active wired connection on the Apple TV 3 is the micro USB cable connection.
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Step 8. Open your computer desktop and double-click the Snow3rd.zip file
The contents of the file will be extracted and a Snow3rd dialog window will appear on the screen.
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Step 9. Click the “Jailbreak” button
The jailbreak process will start and the progress will be displayed in the status bar. This procedure takes a few minutes to complete.
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Step 10. Close the Snow3rd dialog box after the message “Jailbreak Successful” is displayed on the screen
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Step 11. Disconnect the Apple TV 3 from the mini USB cable, and restart the device
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Step 12. Reconnect Apple TV 3 to the computer after restarting, then open iTunes on the computer
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Step 13. Make sure iTunes recognizes the Apple TV 3
If iTunes recognizes the device and displays the Apple TV icon in the upper-left corner of the window, the jailbreak has been completed successfully.
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Step 14. Connect Apple TV 3 to a power source and HDMI cable
Your Apple TV 3 is now jailbroken so you can install and run jailbroken apps downloaded from outside the App Store (via the web).