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Look at the first post there is a link if you wanna try that methodAnyone able to root 12b update.. and how?
You could leave kingo up and just let people know that it can take many attempts.
I've rooted twice already with kingo by itself. Framaroot and saferoot are not needed since they do absolutely nothing to help the rooting process.
It doesn't make sense that some people have had success after running Kingo for hours. If the vulnerabilities have been patched, the exploits won't work - it doesn't matter how many times you try.
Kingo hasn't been patched. It was saferoot and framaroot that were patched. Some exploits with these LG phones take multiple attempts. If we receive another update, kingo and root keeper might be patched though. Then we'll have to ask the root god (Bliss) if he can make a root for us.
As far as I know, only the Kingo developers know which vulnerability it uses for each device. It's likely that it was using the same vulnerability as saferoot for our device. My best guess as to why some have been able to root 12b and some haven't is the users that have been successful had something in place that prevented a proper kernel update and their kernel was still vulnerable. It would be interesting to see the output of uname -r from users who claim to have used Kingo to root 12b.
Like I would give you malware and trojans.. That is ridicules.
But the OP originally said something like "try these steps, let me know if it works". Well that can inadvertently add unnecessary steps that is unverified and could potentially spread malware.Kingo is open source and uses other open source projects in the app. They list all the open source projects they use and saferoot is not one of them even though saferoot is open source as well. They seem to be using an old exploit called ZergRush which they've modified.
In an official LG update all partitions are updated if not the update fails so it would be impossible for the kernel not to be updated. Only partition not updated is userdata. I don't know why kingo works for some and not for others. You would have to look at zergrush to see how it works for an answer.
By official LG update, you mean the FULL kdz update? and not OTA? OTAs are only a few megabytes, and possibly doesn't replace all partitions. Or OTA failed some pre-check for the kernel and skipped it, allowing kingo to root afterwards. Since you mentioned here or another thread kingo worked for you, can you report what 'uname -r' says just so we have notes to compare for those who aren't able to root on 12b using kingo.

I will edit this accordingly when I can confirm this process works other then just my phone. Credit goes to smart for originally posting the steps.
Another root method discovered for 12b here thanks to Nirhazine (i personally have not tested this but its worth a try for anyone willing)
Link
Removed due to many failures to root. will repost when we find a more adequate way to root.
May be able to use kingo by itself may take multiple tries.
For those of you that have gotten it to work good job for those that havent and want to go back to I try this http://androidforums.com/metropcs-t...8-guide-unbrick-unroot-lg-optimus-f3-kdz.html but use http://csmgdl.lgmobile.com/dn/downloader.dev?fileKey=FW857785432109876543213/MS50010i_00.kdz instead of the f3 one
thanks to hubsabubs and duper1 from the f3 side for providing us with these
Have you tried uninstalling the drivers and reinstalling them