The following guide will help Windows users to jailbreak iPhone 4, 3GS, iPod Touch 4G, 3G , iPad over iOS 4.2.1 with Greenpois0n RC5. So, continue reading after the break.
Jailbreak iPad 4.2.1 with Greenpois0n RC5 [Mac], Jailbreak iPod Touch 4G, 3G Untethered on iOS 4.2.1 with Greenpois0n RC5 [Mac], Jailbreak iPhone 4, 3GS Untethered on iOS 4.2.1 with Greenpois0n RC5 [Mac]
If your iDevice on iOS 4.2.1 is already jailbroken through iPhone Dev Team’s jailbreak tool then first restore it to iOS 4.2.1 firmware.
Jailbreak iPhone 4/3GS, iPod Touch 4G/3G, iPad Untethered on iOS 4.2.1 with Greenpois0n RC5 [Windows]
Create a new folder on your PC’s desktop, download Greenpois0n RC5 for Windows and keep it in your created folder
Open your new folder, unzip the downloaded gp_win, then double click on Greenpois0n.exe file
Attach your iDevice to system through USB cable, click on Prepare to Jailbreak (DFU) button on Greenpois0n screen
Greenpois0n will instruct you to put your iDevice into DFU Mode, so follow those instructions carefully
Once your iDevice enter into DFU mode, click on Jailbreak! button, immediately jailbreak process will get start
On completion click on Quit button
After restart of your iDevice Loader app icon will be available on Springboard, so tap on it to launch that
Select Cydia and tap on Install Cydia button
When Cydia will be installed it ask to remove Loader.app from your iDevice, so tap on Remove button and reboot your device by pressing Home button
You will find Cydia icon sitting on Springboard
Enjoy, you have successfully jailbroken your iDevice over iOS 4.2.1 with Greenpois0n RC5 on Windows.