In order to create an account with Pokemon Go, iPhone users could sign in with their Google accounts.
This allows Niantic, Pokemon's developer, full access to Gmail, Google Drive files, anything shraed on Google Photos and more.
If someone were to hack Niantic, all of the information obtained through the account is fair game.
In response to this concern of privacy, Niantic released a statement saying it "recently discovered" the "account creation process on iOS erroneously requests full access permission for the user's Google account."
The company is now working on having only basic Google profile information, like user IDs and email addresses, in order to have a Pokemon Go account.