A new firmware update has been released for the  Nintendo 3DS.

Version 6.1.0-11U available via wireless Internet connection includes the following improvements:

• Further improvements to overall system stability and other minor adjustments have been made to enhance the user experience.

From the very short changelog it seems to be the usual canned message for blocking flash carts. In anycase, the mandatory update is required when using the eShop so be sure to update your consoles before doing so.