It appears that users are being banned from 3DS online services, en masse. There's no direct cause right now, and seemingly no linking factor. This post is meant as an announcement for users, to be wary, and that GBAtemp will keep you updated as soon as more info rolls in. If you have been banned, please post in the thread below, and we will try to keep tabs on the situation. To be extra sure, it can't hurt to turn off your 3DS's wireless capabilities, so you might as well do that for now.
Edit 1: it appears that e-Shop access isn't restricted if you are banned.
Edit 2: A caller to Nintendo reported that the company said this ban is due to "unauthorized software usage".
[11:28:19 PM] Clector: Curiously the page of that error in Nintendo Support website used to have this:Error Code: 002-0102 Situation: You receive the error code 002-0102 when attempting to connect online. What to Do: If you continue to experience this issue, please contact Nintendo by calling 1-800-255-3700. Representatives are available from 6 a.m. to 7 p.m., Pacific Time, 7 days a week.
[11:28:44 PM] Clector: Now it says this: What to Do: If you are experiencing this error code, your Nintendo 3DS family system has been banned due to unauthorized system modifications, play of unauthorized versions of one or more games, and/or connecting to the official game servers in violation of our terms of service. This ban is effective immediately and requests to remove the ban will not be processed.