Protect your Privacy with Private Domain Registrations — Blog — WordPress.com:
"One of the requirements of owning a domain is that you must give your contact details when registering that domain.
Internet regulations require that your name, address, email, and phone number be accessible 24/7 to anybody who wants to see them just by looking up your domain. This rule was created to make it easy to contact a domain owner in case of problems, but it has since been exploited by spammers and marketers to bother people. Your personal information is exposed 24 hours a day, everyday, to anyone, anywhere.
Unfortunately since this information is publicly available it may be used by spammers and marketers to send unsolicited messages, or by others who want to harass a domain owner"