Much like a telephone company, the Internet Corporation for Assigned Names and Numbers (ICANN) maintains a directory of contact information for everyone who registers a domain name. The Whois database contains the name, physical address, email address and telephone number for each registrant.
This database is accessible to anyone with an Internet connection, making it easy for people to contact a Web site owner with legitimate concerns, questions or even offers to buy the domain name. It also establishes a certain amount of credibility for the Web site because it publicly identifies the person responsible for the site.
On the flip side, this public sharing of information causes some concerns. It gives a good deal of information to anyone, legitimate or not. Spammers may collect email addresses off the database, telemarketers can collect phone numbers and identity thieves have a long list of potential victims.
Many Web hosting companies allow you to choose to display your own personal information in the Whois database, or for a small fee, you can use the company as a point of contact to protect your privacy.