SixDegrees.com was a social networking service website that started in 1997 and was based on the Web of Contacts model of social networking. It was named after the concept of six degrees of separation and allowed users to list friends, family members and acquaintances whether registered on the site or not. External contacts were invited to join. People who confirmed a relationship with an existing user but did not go on to register with the site continued to receive occasional email updates and solicitations. Users could send messages and post bulletin board items to people in their first, second, and third degrees, and see their connection to any other user on the site.