Done wrong, this could actually damage your device, as with all roots and mods, you are warned and I am not accountable for what happens.
Also, it is sfhub of AndroidCentral who should get credit for this, this is from his post.
Instead of going through the time to upload my own zip I'll just post the original link here.
Optimus S Auto Root, though, there are a few things to do before starting:
1) Download the ZVH automated rooting package
UNZIP to top-level directory of your C: drive
2) CHANGE THE RECOVERY, Since this is for the Optimus S, the recovery would be different. I used the
GNM Recovery. Rename the img file to "xionia_cwma_12518.6.img" then Go to 'C:\zvhauto\copy2sd\000root' and paste it there, it should ask you to replace the one that is already there, do it.
3) Pre-requisites Checklist
SD card is INSERTED
USB Debugging is ENABLED - [Menu->Settings->Applications->Development->USB debugging]
USB Storage Mode is OFF - [Drag down the notification bar to check]
LG USB/Android drivers are INSTALLED
Phone is connected to USB port and recognized
Phone is turned ON
Phone screen is UNLOCKED - [Menu->Settings->Applications->Development->STAY AWAKE]
4) Run the ZVH automated rooting package
From PC command prompt, run "runfirst" and select Option A (will install persistent root and Xionia CWMA recovery):
(if you have an aversion to typing, you can use file explorer to navigate to C:\zvhauto and double-click on RUNFIRST.bat)
Note #1 - You may see a message in your notification bar saying "SD card safe to remove", this is expected, please IGNORE
Note #2 - If you get stuck waiting for the phone to connect, REBOOT your phone AND PC and try again.
(don't worry if there is an error with Busybox, the directories are different, and it's not really necessary)
5) You should be rooted. Reboot. Try typing in cmd:
Please let me know if it works or not. I might try to upload my own edit of this specifically for the OM, but I guess this can do for now. Thanks, Hope it works.