As a rule, Amazon tends not to update their older Kindle models. For example, the most recent Kindle firmware update (v5.7.2) was only made available for the 2013 Kindle Paperwhite and the more recently released Kindle Voyage and basic Kindle.
But now it appears Amazon is making an exception to this policy.
Several sources have reported that Amazon is sending out emails demanding that Kindle owners update their ereaders. The email includes instructions on how to download the update, as well as this ominous warning:
If you do not update the devices' software by March 22, 2016, you will no longer be able to access Kindle services or get the update via Wi-Fi or a wireless connection. To resume access, you will need to manually update the software on each of your Kindle devices. Please visit our Help page for more details on how to update automatically: www.amazon.com/ku2016
I have not received this email, but I'm told that Amazon is sending it to all Kindle owners, including people who own older Kindle models like the Kindle DX, original Kindle, and the Kindle Keyboard.
While that would appear to be a mistake, members of MobileRead have investigated and discovered that Amazon has released updates for the older Kindle models, including the original Kindle (which launched in November 2007).
The update for the original Kindle is only 12KB in size, and according to the techie who unpacked the update it only makes a small change to a single folder (/opt/usr/java/lib/security/cacerts).
Based on the context (edit: and the) this is clearly a security update of some kind. It's most likely one which affects how the Kindles communicate with Amazon's servers.
So if you get a notice, you should update your Kindle immediately. (Better yet, why wait?)
P.S. Did you get the notice, and have you acted on it? (Not everyone has received it.)
image by Strupey