For personal protection on the internet you should not let anyone know your password, or user name. If for any reason you have to put your birthday or other personal information on a website use all privacy settings you can. Don't let anyone know your password, if neccasary change it every now and again. If you are logged onto (let's say) Facebook on somebody else's iPod, computer, or other device make sure you log out!
When you use a password don't make it something obvious and easily geuss-able. On facebook or any other site of the sort don't put your town, or you address. THERE ARE CREEPERS!!!