There have been many MiceChat threads in the last couple years discussing NextGen in general and MyMagic+ in particular. Threads in which some posters expressed concern about the security of customers' personal data.
Such posters were piled on with "you're just paranoid, Disney knows what they're doing."
In fact, as the rollout of MyMagic+ and the mouse-snafus in other areas of their operation have made plain, Disney doesn't. From the MiceAge article about MyMagic+...
"In the limited roll out of MyMagic+ and My Disney Experience, the most egregious issue has been problems with the new website. Many guests have reported seeing another family’s personal information. Reports have even stated that upon refreshing the website, a third family’s itinerary will appear. Guests are able to make changes to another family’s itinerary, potentially disrupting multiple vacations. On a smaller scale, dining reservations are not always syncing properly with a guest’s account and tech support has been unable to repair many of these issues."
Unfortunately, Disney's MyMagic+ customers may learn the hard way that their personal data is not safe with a corporation that values quick-and-cheap solutions over longterm and top quality. A corporation that is so topheavy with conflicting departments that it couldn't roll out an updated Disneyland monorail that fit on its own track.
When data security problems arise, don't expect truth and transparency from Disney. Expect instead the same dismissive arrogance and PR-speak displayed in Bob Iger's letter to Representative Edward Markey:
"The recent announcements of MyMagic+ and Fastpass+ have raised concerns in the fan community over Disney’s priorities. These concerns were shared by United States Representative Edward Markey, and led to a methodically crafted, yet somehow juvenile response from CEO Bob Iger."
"...Perhaps the biggest concern amongst the fans is the loss of privacy and the transition to Fastpass+. Representative Markey asked pointed questions regarding how the collected data would be used, and if people that opted out of this data collection would see longer lines at attractions. These questions were not sufficiently answered, and the response to date has only been that guests will get a more convenient experience if they participate in MyMagic+."
"A more convenient experience" for Disney's beancounters, that is.
For Disney's customers... caveat emptor.