We have an app in which user register. After registration they are able to connect their account to Facebook using the linkuserwithfacebook method, to use their friendlist, avatar etc. Now, while in production for about 6 month, we discover different users having the same facebookID. We think the different accounts are used by the same person. My question is:
Is there a way to find out if a facebookID is already used by an other user?
We would try to prevent future duplicate use of FacebookID. So I hope someone can help me on this.