Apple today released iOS 4.3.1 for iPhone 4, iPhone 3GS and iPod Touch 4G, iPad 2 and iPad. After updating to iOS 4.3.1, you might face incompatibility issues with some of your favorite apps forcing you to return to older  firmwares – iOS 4.3, iOS 4.2.1 or iOS 4.1. If you inadvertently updated your device to iOS 4.3 and would like to downgrade back to iOS 4.3, iOS 4.2.1 or iOS 4.1, follow the steps below:

VERY IMPORTANT: This Guide is only for those who have already saved the ECIDs with SHSH to Cydia Server for iOS 4.3, 4.2.1 or 4.1. Those who haven’t should not follow it.

Guide to Downgrade iOS 4.3.1 to 4.3 / 4.2.1 / 4.1 Firmware

Step 1: Download the old firmware files to which you wish to go back to. (Download links:iOS 4.3,  iOS 4.2.1, iOS 4.1)

Step 2: Navigate to the path c:\windows\system32\drivers\etc\ and open the hosts file in a notepad or wordpad. MAC users can navigate to the path “/etc/” and open the hosts file with TextEdit.

Step 3: At the end of file add the string 74.208.105.171 gs.apple.com useful to redirect requests for certificates for authenticity that iTunes will make to the Saurik server. You may follow the steps below to do so.

Windows users

• Open Notepad with administrator privileges and then right click on the icon of notepad and click on “Open as administrator”
• Now that Notepad is open Go to folder C:/WINDOWS/system32/drivers/etc and open the file
• Add the following line at the end of the document and save it: 74.208.105.171 gs.apple.com

Mac users

• Navigate to Go -> Go to Folder and enter the path /etc
• Open the file hosts with TextEdit, add the following string 74.208.105.171 gs.apple.com and save the file to your desktop.
• Now return to the previous folder by following the same method and copy the text within this file by replacing the original file (If prompted for a password enter it and click OK)

Step 4: Set up your device in DFU mode (not into Recovery mode). DFU mode is a mode where the iPod Touch, iPhone will be made to force a restore of the firmware into whatever version firmware it is given.

Getting your iPod Touch or iPhone into DFU mode is somewhat tricky, and it may require some patience and practice because timing is essential to get it to DFU mode and not into recovery mode.

• Open iTunes and connect the iPhone to your Mac.
• Press and hold the Home button and the Power button at the same time.
• After exactly 10 seconds release the Power button. Continue holding the home button until computer recognizes your iPhone.

After iTunes recognizes the iPod Touch/iPhone, let go of the Home button otherwise it will go into recovery mode and you will have to do the entire DFU process over again. You will know when you have put your iPod Touch/iPhone correctly into DFU mode when the display is blank and that you do not have anything on your device.

Step 5: Now, restore your iPhone, iPod touch or iPad to the firmware you downloaded in Step 1. Select the right device icon from the iTunes sidebar. Now press and hold left “alt” (option) button on Mac (Left “Shift” button on Windows) on the keyboard and then click on “Restore” (Not “Update” or “Check for Update”) button in the iTunes and then release this button. This will make iTunes prompt you to select the firmware file. Select the right ipsw file and click on “Open”.

Step 6: Be patience at this point! Your iPhone screen at this point will be showing a progress bar indicating installation progress.

In-between the ongoing process iTunes might show the following error messages: “The iPhone could not be restored. An unknown error occurred (1004).” and “iTunes has detected an iPhone in recovery mode. You must restore this iPhone before it can be used with iTunes.”

Press “OK” to continue. This is absolutely normal. No need to worry.

Step 7: Your iPhone at this point will be stuck in Recovery Mode, showing that “Connect to iTunes” screen.

To exit your device from Recovery Mode, use TinyUmbreall (Windows/Mac).

Your iPhone will now reboot normally. You have now successfully downgraded iOS 4.3.1 to iOS 4.3, 4.2.1, 4.1 firmware. You can follow the normal guides to jailbreak. If you have downgraded your device to iOS 4.3, you can use either sn0wbreeze (for Windows) or PwnageTool (for Mac). iOS 4.2.1 or iOS 4.1 users can use greenpois0n for untethered jailbreak.

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