[HTC Desire 601] -Duir-:
So, it's impossible to write a guide that will guarantee S-OFF but this will at least help to give you the best possible chance.

If you encounter issues attempting S-OFF using Windows, try it under Linux. Users have reported successful attempts with their device on Linux when Windows previously failed them. Easiest method if you don't already have Linux installed somewhere is to setup a bootable USB flash drive and run Linux from it. Details on that can be found here

BEFORE YOU DO ANYTHING MAKE A BACKUP UP YOUR DEVICE (INCLUDING BOOT.IMG)

Instructions for S-OFF (from rumrunner website):

Stuff in green is my on additional information/notes.

Prerequisites

32-bit Linux (Ubuntu is preferred)

Live CD’s are fine.

Live USB is fine.

Native install is fine.

VM’s are unsupported.

64-bit Linux may work with 32 bit libraries, but is unsupported.

Or Windows

HTC drivers installed and working – fastboot AND adb drivers

HTC sync removed (not closed – REMOVED)

Install HTC Sync from here (it will install drivers and the sync manager app) and then remove the Sync Manager app (See attached picture).

All other phone software removed or disabled (Samsung Kies, PDANet, etc.)

VM’s are unsupported.

ALL firewalls and internet security applications should be totally disabled. If you get stuck with rows and rows of dots during the connection test process, it’s network filtering or other network issue!

This includes anti-virus applications as well.

Do NOT clutter our support channels with support requests on an unsupported OS configuration.

A working internet connection

USB debugging enabled on your device

Fast boot disabled on your device (settings -> battery -> UNcheck “fast boot”)

Your device must be HTCDEV unlocked or rooted unless using rumrunner with a device blocked by htcdev (e.g. m7wlv)

Additional that weren't covered:

Backup your device

Flash an unsecured kernel

ZARA_CL: KitKat / Jelly Bean

ZARA_UL: KitKat / Jelly Bean

Instructions

Once you confirm you meet the above pre-requisites, it’s time to get started.

Read all of the directions on this page before proceeding to the downloads page.

Ensure device is booted to android with usb debugging enabled.

USB 2.0 ports are preferred.

USB 3.0 ports are known to cause connectivity problems

You should not be connected using any hubs which may cause connectivity issues

Use the original HTC usb cable or a cable that you know to work with adb and fastboot on this device

Ensure that lock screen security is disabled on your device.

no passcode lock

no pattern lock

no face lock

Download rumrunner for your device. Linux users – this must be to your ~/Downloads directory.

Linux users – do NOT try to download or run it from your Windows/Mac drive or a USB drive that is not formatted for native Linux use. It won’t work!

Download page is here. You want rumrunner_HTC_0.5.0 from the HTC Universal Downloads section.

Extract the archive

tar -zxf rumrunner<device>_<version>.tgz (Linux)

Unzip the file rumrunner<device>_<version>.zip (Windows)

Execute soju: linux: sudo ./soju windows: double-click soju.exe

Windows: Right-Click soju.exe and select "Run as administrator"

Agree to the terms and conditions you are prompted with in soju

Allow the exploit to do its work.

Your device will reboot several times throughout the process

If the process gets to "Pouring..." and your device boot-loops you have achieved S-OFF - This is a known issue with Jelly Bean devices and I don't know if it is a problem on KitKat. There is a file (/system/bin/hcheck) that causes a boot-loop when you are UNLOCKED and S-OFF.

If you get this problem do the following:

Hold down the power button until your phone turns off

Once off, press and hold the volume down and power buttons until your phone turns on

It will boot into the bootloader allowing you to verify you are in fact S-OFF

Press volume down to highlight "Recovery" and then press power

Once in recovery, mount the system partition

Then open the file manager. (in TWRP tap Advanced and then File Manager)

Navigate to the /system/bin folder and scroll down until you see the "hcheck" file.

Select the hcheck file and either delete or rename it.

Reboot the device and then...

Profit

This is pretty much all the extra stuff I can think of to help make your attempt to S-OFF your device go smooth.

Remember, if you're trying it through Windows and it just doesn't want to work, try Linux.

Unfortunately, I can't provide any pointers to those who try the Linux method as I am just not a Linux person.

GOOD LUCK!