Some privacy concerns. Players can opt in to Apple's Game Center to track scores and achievements, and for some games, challenge friends. Players can send and receive friend requests using an email address or Game Center nickname, revealing the first and last name associated with each party's Apple ID and, in the case of email requests, the sender's email address. With iOS 5, players can opt to have a private or public profile, which can include a photo. With a public profile, your real name is visible to all other players, and Game Center will recommend you to other players using your real name. With a private profile, only your friends can see your real name, and Game Center will not recommend you to other players.