 Open Diary was launched in October 1998; LiveJournal in April 1999; Ryze in October 2001; Friendster in March 2003; the corporate and job-oriented site LinkedIn in May 2003; hi5 in June 2003; MySpace in August 2003; Orkut in January 2004; Facebook in February 2004; YouTube in February 2005; Yahoo!360° in March 2005; Bebo in July 2005; the text-based service Twitter, in which posts, called "tweets", were limited to 140 characters, in July 2006; Tumblr in February 2007; and Google+ in July 2011.The variety of evolving stand-alone and built-in social media services makes it challenging to define them.