A social network service focuses on building online communities of people who share interests and/or activities, or who are interested in exploring the interests and activities of others. Most social network services are web based and provide a variety of ways for users to interact, such as e-mail and instant messaging services.

Social networking has encouraged new ways to communicate and share information. Social networking websites are being used regularly by millions of people.

While it could be said that email and websites have most of the essential elements of social network services, the idea of proprietary encapsulated services has gained popular uptake recently.

The main types of social networking services are those which contain category divisions (such as former school-year or classmates), means to connect with friends (usually with self-description pages) and a recommendation system linked to trust. Popular methods now combine many of these, with Facebook widely used worldwide; MySpace, Twitter and LinkedIn being the most widely used in North America; Nexopia (mostly in Canada); Bebo, Hi5, StudiVZ (mostly in Germany), Decayenne, Tagged, XING;, Badoo and Skyrock in parts of Europe; Orkut and Hi5 in South America and Central America; and Friendster, Multiply, Orkut, Wretch, Xiaonei and Cyworld in Asia and the Pacific Islands.

There have been some attempts to standardize these services to avoid the need to duplicate entries of friends and interests (see the FOAF standard and the Open Source Initiative), but this has led to some concerns about privacy.

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