Getting a device rooted is always a big deal. After all, the vast majority of cool stuff created by our developers requires root access. As such, devices get rooted pretty often. However, then there are firmware updates. In most cases, it’s a small update, and rooting again is no big deal. Other times, it’s going to a whole different version of Android. Many devices have received official updates from Gingerbread to Ice Cream Sandwich, but once there, there’s still going from 4.0.3 to 4.0.4. For users of the Sony Xperia Arc, Pro and Arc S, there is no need to worry because 4.0.4 has already been rooted.
The method was originally posted by XDA Senior Member Overlo4d as a way to help get Xperia Pro, Arc, and Arc S users to rooted 4.0.4. However, the method could be a tad convoluted for some, so XDA Forum Member panicc.co created an easier guide for the more novice users out there. The process itself isn’t so bad. Users will need Flashtool 8 to get started, and a couple of downloads depending on where you’re coming from. Once all the files are in place, users simply flash the pre-rooted kernel.
For additional information, you can find the Arc, Arc S, and Pro root tutorial in the original thread, and the version that explains all the steps in the second thread.