Board Thread:Question and Answer/@comment-110.159.33.212-20150516120603/@comment-29547733-20161202224537

It's because the emulator is most likely rooted, thus it shares the same device ID as everyone else who has that version of the emulator installed hence why you can access someone elses account. You can still use an emulator but use an offline version or a non rooted version and you should be fine, it's what I do.

PS: Please don't mess with their account, I accidentally lost mine to someone else going back and they wasted my hard earned ABB rings on slimes before I could retrieve the account in time to prevent anything happening. -__-