Apple has just released a minor software update for Apple TV 3. According to the official release note, Apple TV Software Update 7.2.1 only includes “general performance and stability improvements.” However, Apple also posted a security document listing a whole bunch of security fixes included in the new firmware.
If you don’t have automatic updates turned on, go to Settings -> Software Update and select “Download and Install” to apply for the update.
Back in January Apple released the first beta of tvOS 9.2 for Apple TV 4 that adds Podcasts app, support for Bluetooth keyboards, folders for grouping apps, new Siri languages and a new app switcher. The final version of tvOS 9.2 is expected to be released in March.