People always have warned to go into emuNAND as fast as possible so that I don't get the update offer but now I do get the update offer even when I'm offline.
So is it bad?
What can I do about it?
This is what begins the nagging:
1) The system is running sysNand
2) The system is in sleep mode
3) The system has access to the internet (either through a saved connection in Connection Settings, or through a SpotPass hotspot like at McDonalds)
If all those conditions are met, and an update is available, the system will download the update and then begin nagging you to install it. It will not install it automatically without confirmation. Personally, I'm only ever in sysNand long enough to get to emuNand, so #2 never applies for me, so I don't get the nag.
How to get rid of the nagging:
1) Have the system completely powered off
2) Hold L+R+A+Up (on D-Pad)
3) While holding all four buttons, turn on the system
This enters Recovery Mode, a special mode made for recovering from a corrupted system update install
4) Cancel or power off the system
What Recovery Mode does:
1) Deletes any downloaded update
2) Provides a menu option to download and install the latest update
As long as you hit cancel or turn off the system without doing anything, it will not change anything on your system. That means it does not remove the installed mset.cia (because that would require downloading and installing the latest version of mset), it does not update your system. But since it deleted the downloaded update, you no longer have a pending update for it to nag you about.
However, you cannot enter Recovery Mode when booting emuNand. The process that boots emuNand skips the power-on checks that look for button combinations like Recovery Mode. I believe I remember seeing a thread that detailed the process of removing the nag from emuNand, but it was fairly involved. And since you likely have your Network Connections set up in emuNand, you're probably going to hit it again fairly quickly. There are also guides on how to block access to Nintendo's update servers, though it would only work for your personal, home internet connection. But at least if you accidentally update emuNand, it's not the end of the world, as long as you have a recent backup.
Damn... I don't want sysNand to update.
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So, am I ok as long as my 3DS is open and on the "Finished Update, push to restart" screen?
When you restart, it will likely restart the whole system, leading it to boot sysNand. It won't update sysNand, just reboot the system. Only emuNand will have been updated. Just run your exploit of choice, and then once in emuNand, go into System Settings to verify your version.
Whenever you are updating emuNand, ALWAYS make a backup first, then check to make sure you have GW3D in front of your System Version number. Always update only through the System Settings app, never through a card or the eShop or anything else.