Apple has released new firmware for the AirPort Extreme Base Station, in response to a security flaw that could compromise a machine. The flaw only affects the Base Stations that support 802.11n (pre-n, actually), and don't effect earlier models that do not have it. The flaw relates to IPV6 traffic, which makes it a relatively low on the scale of how likely it is to be compromised, but is there nevertheless.
Apple posts instructions in the security notice on how to update the firmware. A lesser issue is also fixed in the update, one that can expose password-protected files (or at least their names) to devices connected to it. The bug in this case doesn't allow someone to download or open the files, merely check the their names. In either case, updating the firmware is exceedingly simple and is a good idea if you own one.