The 3.2rev03 update added a single title, IOS37, to the Wii. This was the first fix to the signing bug, although nothing used IOS37 yet. However, many people began to panic due to this.
The intention of this update is unknown, although it may have been to discourage Datel from releasing their Freeloader outside PAL regions, as it could cause bricks without voiding console warranty.
This update has also led to quite a few applications being developed to prevent the update from causing problems, most of which were completely pointless. However, some, such as PatchMii and Menuloader, did everything safely and benefitted homebrew.
Interestingly, IOS37's build date seems to be before Trucha Signer was released. While it may seem like Nintendo/BroadOn found the exploit on their own, they also messed with the build date on IOS30 in 3.3 to make their ES fix look like it belongs in IOSP. This was also most likely Nintendo trying to scare the homebrewers by manually changing the build date.
↑ 1. https://hackmii.com/2008/04/the-doghouse-wiisystemmenu-wadpatcher/
↑ 2. https://hackmii.com/2009/06/ios-history-build-process/