An unofficial 4.2.1 Jelly Bean update for the Samsung Galaxy S3 was making the rounds in the internet.

You can download the I9300XXUFMB3 FW 'leaked' firmware from SamMobile now to start playing around with Android 4.2 on your Galaxy S3. The fan site provides step-by-step instructions to help you install the custom ROM on your Galaxy S3.

Some of the new features offered by the Jelly Bean update are lock screen, new widgets, an improved Notification Center, Daydream, and Voice Command.

Other enhanced features include Google Now, swiping across to the camera, a look at the homescreen and TouchWiz. There is also a difference in brightness setting and how to adjust it, notifications, toggles such as Wi-Fi hotspot and then the video moves onto Settings, where some slight differences are noticed although nothing major.

We also see Samsung Cloud settings, lockscreen settings and settings for the lockscreen widget and then there are some details of voice commands.

"We have FULLY TESTED this firmware and this firmware works perfect as any other official firmware," SamMobile said.

However, some users commenting on the unofficial release noted minor bugs and glitches occurring after they flashed the custom ROM to their handset. Thus, users are warned to install the custom ROM at their own risk.

Here is the step-by-step procedure in installing the Androidv4.2.1 Jelly Bean leaked firmware to your Samsung Galaxy S3.

  • Unzip the file
  • Open Odin 3.04 (already included in the firmware package)
  • Restart phone in download mode (Press and hold Home + Power + Volume down buttons)
  • Connect phone and wait until you get a blue sign in Odin
  • Add I9300XXUFMB3_I9300OJKFMB3_HOME.tar.md5 to PDA
  • Make sure re-partition is NOT ticked
  • Start flash, sit back and wait a few minutes.
  • If you encounter any issues with the firmware (Any FC, Bootloop etc)
  • Boot into recovery mode (Home+power+vol up)
  • Choose to wipe/factory reset. This will erase all of your data.
  • Choose reboot.

Samsung is expected to release an official Galaxy S3 Jelly Bean 4.2 update on 14 March along with the unveiling of the new Samsung Galaxy S4.