Though very personal and often not freely shared, your name, phone number, mailing address and email address all belong to you but are most often used by others. The knowledge of each of these helps the people who wish to communicate with you distinguish you from others and reach you directly.
Though giving your first name to a new acquaintance is friendly, be careful with whom you share your personal information, especially online. Many thieves rely on the openness and honesty of their targets to take advantage of them and steal their money or identities. By keeping such personal information reserved for those you truly know and trust, you keep yourself safe from those who wish to harm you.