Apple has updated its AirPort Extreme firmware to version 5.3 for Mac OS X and Windows networks.
The 1.5MB download is available from Apple's support Web site and is not for use with the original Graphite or Dual Ethernet/Snow AirPort Base Stations.
Explanatory notes on the software available from Apple state that the release "includes support for the Wi-Fi Protected Access (WPA) specification for the base station." WPA increases data-protection and access-control on wireless networks.
The release also offers "performance improvements" between wired and wireless network clients and improves USB printing performance.