Well, we're proud to say that Saulius and I have managed to downgrade the zunes firmware with nothing but a computer and a zune, and no problems at all!
no ZIFF cables needed, nothing.
safe to say, we believe that the first firmware mod is on its way, since we have nearly gotten the zune to transfer modded firmware onto itself.

[...] We managed to get two things:

1. Zune Certificate Authority
2. The Encryption Key

and we never tried to make our own firmware, we simply changed around the old one.
of course the 'sig check' will nullify this again, but the zune itself doesnt check for a sig, it uses a different method.
and there is really no need for a crack...our method is much much simpler than that.

[...] i double checked
theres more than one key
i got the thumbprint too

[...]the zune program checks for the exact file size of the file before sending it and booting it onto the zune. that is one of its ways of verification. if you can keep the file size proper, you are well on your way.

There are three possibilities here:

• This is nothing more than a fake forum post.
• They have something, but its not what they think it is. Downgrading the official Firmware could mean nothing.
• This is real and is the door to custom firmware updates on Zune! 

We'll definitely keep an eye on this and let you know of any progress. Talking to Shailigum last week, told me that in the next few hours/days they will announce more. Just wait and see.

(Thanks Reyer Sikkel for sending this).