A social networking site is an on-line service that attracts a society of subscribers and provides such users with a multiplicity of tools for distribution personal data and creating subscribers generated content directed to a given users interest and personal life. Operators of online social networks are gradually giving out potentially sensitive information about users and their relationships with advertisers, application developers, and data-mining researchers. Some criminals too uses information gathered through membership profile in social networks to break peoples PINs and passwords. In this paper, we looked at the field structure of membership profiles in ten popular social networking sites. We also analysed how private information can easily be made public in such sites. At the end recommendations and countermeasures were made on how to safe guard subscribers personal data.