It used to look for any public key which meant it would use the one added by the jailbreak. They’ve now altered it so that it specifically only checks the two Amazon Kindle public keys. This means all hacks will NOT be able to be installed.
The good news is if you already applied the hacks, they’ll continue to work. My custom screens are still working fine and I don’t even know when the 3.1 update was applied to my Kindle — I discovered it just a few moments ago when I checked my Settings screen.
The bad news is if you wanted to apply the hack but Amazon already updated your Kindle, you’ll have to wait until someone finds a new workaround — but fortunately someone is already working on it. Here’s hoping this setback is only temporary.
reposted from BookSprung