Quote (defectivebydesign.org)
The Nintendo 3DS comes with Terms of Service (TOS) that should not be accepted. To enforce these terms, Nintendo uses Digital Restrictions Management (DRM) technology. Because of the Digital Millennium Copyright Act (DMCA), users are legally prohibited from modifying their devices to block Nintendo's nastiness. This combination of legal and technological restrictions makes the Nintendo 3DS dubious, devious, and defective. This page outlines some of the nastier parts of the DRM-enforced TOS.
The Nintendo 3DS keeps track of every game you play, along with any data or information created while using the device. This includes personal data such as any name, address, or other information you enter; as well as "age, gender, geographic area, game play data, online status, Nintendo 3DS System serial number and device ID, device certificate information, cookies, Friend Codes, wireless access point information, Internet Protocol ('IP') address, and Media Access Control ('MAC') address" (to quote the Nintendo 3DS System Privacy Policy). Further, they collect all "User Content," which they define as all "[...] comments, messages, images, photos, movies, information, data and other content" (Chapter 6, Nintendo 3DS End User License Agreement).
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http://www.defectivebydesign.org/nintendoAs a person who's concerned about his privacy, this is pretty much enough for me to never buy another Nintendo product ever again.