The International Olympic Committee has issued rules for athletes using social media at the 2012 London Games.
The IOC ''actively encourages'' competitors to ''post, blog and tweet their experiences.'' But it warned that if rules are broken it can withdraw accreditation, shut down online operations and start legal action for damages.
Athletes can't use Twitter, Facebook or personal blogs for commercial or advertising purposes or share videos filmed at Olympic venues.
At the 2010 Vancouver Games, United States alpine skier Julia Mancuso was asked to stop online merchandise sales after her double silver medal-winning performances generated interest in her official website.
Games-time rules - which apply from July 16-Aug. 15 - also protect the rights of Olympic broadcasters and sponsors.
''Postings, blogs or tweets should be in a first-person, diary-type format and should not be in the role of a journalist,'' the IOC document stated. ''Participants and other accredited persons cannot post any video and/or audio of the events, competitions or any other activities which occur at Olympic venues.''
The IOC also urged athletes not to comment on their opponents or reveal confidential information, and to conform to the Olympic spirit and charter.
Posts, tweets and blogs should ''be dignified and in good taste, and not contain vulgar or obscene words or images.''
''Apart from that, we want people to share as much as possible their personal experience of the games,'' the IOC said.
The IOC has drawn up the rules in the aftermath of violations during the last Winter Olympics.
''Unlike in Vancouver, where the rules were adapted to fit changed circumstances, the rules in force in London have been properly codified,'' the IOC said.
