Apple just updated the Wi-Fi firmware for its late 2012 Mac systems, named with Mac Wi-Fi Update 1.0. The update mainly improved the compatibility of the new Mac systems while using the 5GHz band in Wi-Fi connection. The 5GHz Wi-Fi band has better signal quality and lower signal interference, thus to provide more smooth network connection for people to surf the internet. The update is available for free downloading from Mac App Store, in less than 2MB.
You can check the detailed description given by Apple below:
"About Mac Wi-Fi Update 1.0
This update is recommended for all late 2012 Mac systems. This update improves compatibility when using the 5GHz band in Wi-Fi.
Boot ROM or SMC Version Information: To confirm the update has been applied, the CFBundleVersion string of the AirPortBrcm4311.kext will need to be checked.
New driver delivered in update: AirPortBrcm4331.kext CFBundleVersion = 612.20.15
Reference download link: download Mac Wi-Fi Update 1.0