IOS58 Installer does one thing, and one thing only – download and install IOS58 from the Nintendo update servers. This process does not involve any system-critical parts of the system, and is completely safe. IOS58 is required for USB 2.0 support in homebrew applications and is the default IOS used by HBC 1.0.8+. It is included in System Menu 4.3, but those who do not wish to update to 4.3 can just run this installer to get the benefits of IOS58.

http://wiibrew.org/wiki/IOS58_Installer