If you left your 3DS on overnight you may have spotted that welcoming blue LED shinning bright. If you did on opening your handheld you'll be asked to install a newly downloaded System Update.

The latest system software version is now 4.2.0-9E (E in Europe, U in the US and J in Japan).

Unfortunately it is not a major update of the system software with no new features added.

The Nintendo.co.uk site lists the update simply as

● System stability improvements and other adjustments
Further improvements to overall system stability and other minor adjustments have been made to enhance the user's experience.

"System stability improvements" is Nintendo's usual way of saying they've patched up some holes in the firmware that Homebrewers and hackers may have been exploiting.

According to GoNintendo and based on a translation of Nintendo Japan's site the "other adjustmets" is:

- more character options for your password when storing credit card data on eShop

If your 3DS did not automatically download the new update itself you can manually update your system by going to the Settings App then "Other Settings" and scroll to the 4th page to find "System Update".