The guys at Team Twiizers have released HackMii beta 5, which will work on 4.2, but they still recommend NOT upgrading. They explained that Nintendo's boot2 upgrade sometimes causes bricks on Wii's that are innocent and they are deleting replies that bash Nintendo as a result. Darn Nintendo. Anyway, please don't update through Nintendo, use a safe updater like this one instead.
I AM NOT GOING TO LINK YOU, AND NONE OF YOU LINK TO HOMEBREW-RELATED SITES OR DISCUSS IT, GOOGLE IT OR GTFO
If you are already on 4.2 by accident, the new installer will work. BUT YOU MIGHT BRICK.
If you want to upgrade to 4.2 (why?), use the installer before the System Update.
If you are at 4.1 or below, STAY. DON'T UPGRADE ANYWAY. IF YOU DO, NOT THROUGH NINTENDO.
If you've been affected and/or bricked, please read: http://kotaku.com/5372065/wii-update-42-is-killing-wiis-dead (Thanks Xyro!)
Update about New Super Mario Bros and updating:
I AM NOT GOING TO LINK YOU, AND NONE OF YOU LINK TO HOMEBREW-RELATED SITES OR DISCUSS IT, GOOGLE IT OR GTFO
If you are already on 4.2 by accident, the new installer will work. BUT YOU MIGHT BRICK.
If you want to upgrade to 4.2 (why?), use the installer before the System Update.
If you are at 4.1 or below, STAY. DON'T UPGRADE ANYWAY. IF YOU DO, NOT THROUGH NINTENDO.
If you've been affected and/or bricked, please read: http://kotaku.com/5372065/wii-update-42-is-killing-wiis-dead (Thanks Xyro!)
Update about New Super Mario Bros and updating:
Attention!
NSMB Wii will NOT update your wii to 4.2!
I tried it myself. I bought a CD, played it when my wii was 4.0, it told me to make a system update. It was like dropping a 100-ton brick on my anticipation, but I wasn't going to let some silly update prevent me from playing my new game, so I made a backup of my wii using BootMii, and was prepared to use Brawl to reinstall the HBC (or use Gecko through brawl, either way works), and updated.
However, I didn't go to 4.2. I checked the Wii Settings and I was at 4.1! NSMB Wii will force you to update, that is true. But not by going through WiFi or internet! The Update is inside the CD itself. If you get a message to update your Wii, update it through the Disc Channel instead of going to system update. You will be able to play NSMBW with 4.1, and I know I am able to (currently at world 8-7 after using warp cannons lol). I think they got the message that 4.2 sucks **** after it bricked so many innocent Wiis, either that or NSMBW was released too soon after 4.2.
I'm still perfectly able to use music and texture hacks alongside with BBrawl, and also enjoy NSMBW at the same time.