Amazon:

Customers using an outdated software version on Kindle e-readers require an important software update by March 22, 2016 in order to continue to download Kindle books from the Cloud, access the Kindle Store, and use other Kindle services on their device.

Most of you probably have already updated but keep in mind those who may not be as technically knowledgeable as you are. I’ve already told 4 Kindle-using friends about this because they had no idea there was any kind of issue.