Shortly after Nintendo launched a new Wii firmware update that blocks users from running the homebrew-enabling Twilight Hack, folks immediately began work on investigating the update, uncovering a bug that allows them to bypass Nintendo's savedata check and run the hack without issue.
According to Bushing, Nintendo wrote a set of functions that specifically checks savedata pertaining to Zelda, nothing else. Seems rather foolish, considering that other Wii titles could very well have a similar save exploit.
The code in question went under extensive testing for nearly three months judging from the provided timestamps. Further information can be found in the four updates detailed on the page linked above.
No word on when we can expect a fix as of yet, but Bushing is still recommending to not update your console at this time.