Users have been reporting from all corners of the Internet that the Wii firmware 4.2 update has a chance of “bricking” or ruining unmodified consoles. The firmware update also disables applications used to run homebrew, like the Homebrew channel.
The bricking problem appears to occur while the update is loading so if you already updated your firmware you should be fine. However, if you didn’t update you may want to wait for a more stable firmware update. The only thing you’re missing out on is connecting to the Wii Shop channel, which now requires firmware 4.2 to use.
If you were unfortunately affected by faulty firmware Nintendo tech “NOA_TECH_JANE” says you can send your console to them and get it fixed for free – providing it’s unmodified.