How to find out which hack was applied? And how to remove it?

[Starko]

I have K3 with firmware version 3.1.

I remember that long time ago i installed a hack to prevent Amazon automatically updating firmware. Other consequences are that i can not receive any book by mail and i can not download any .mobi files from my Dropbox. That leaves me with USB sideloading as the only option.

I would like to undo that hack but have no idea what hack it was and how to uninstall it!

Any ideas anyone?

PS.

I found a folder on the Kindle called "jailbreak". Inside that folder there are two files:
README

This jailbreak allows you to choose either Amazon updates or hack updates.
Amazon updates may and will prevent future jailbreaks so install with caution.
Hack updates can brick your Kindle so install with caution.

To use Amazon updates, create a blank text file with the name: AMAZON_UPDATES
in this folder and delete any other file.
To use hacks, create a blank text file with the name: HACK_UPDATES
in this folder and delete any other file. (This is default.)
~Jailbreak by Yifan Lu (http://yifan.lu/)~
~Parts taken from "Updates Provider hack" by dsmid~

and an empty HACK_UPDATES
Both files are created on 22-2-2011