Do you have an older Kindle, forgotten in a drawer? Take it out, charge it and turn it on today or tomorrow at the latest. Otherwise, it will lose its WiFi connection function, useful for downloading new books or for… updating your software. Only those Kindles that have been lying around the house without being used for a while are at risk, because every time it connects to the net, the e-reader updates itself with the software version.
This new update affects all models older than the Paperwhite 2012 (full list here) and it's easy to do. It just needs to be connected to a WiFi network with internet access.
If you don't update by tomorrow (March 22) there is still hope, even if you get the message „"„Your Kindle is unable to connect at this time. Please make sure you are within wireless range and try again. If the problem persists, please restart your Kindle from the Menu in Settings and try again.”"You will need to resolve the issue manually by connecting your Kindle to your PC, according to the instructions here.
Another reason to pick up a book from time to time.