(CNN) -- Fifteen countries were named as "Internet enemies" on Wednesday as press freedom campaigners called on Web users to join a 24-hour virtual protest condemning cyber-censorship.
Avatars gather in a virtual Tiananmen Square.
The online demonstrations in virtual locations including China's Tiananmen Square, Cuba's Revolution Square and North Korea's Kim Jong Il Square were taking place to mark the first Online Free Expression Day, Reporters Without Borders (RWB) said in a statement.
"We are giving all Internet users the opportunity to demonstrate in places where protests are not normally possible," the statement said.
"At least 62 cyber-dissidents are currently imprisoned worldwide, while more than 2,600 Web sites, blogs or discussions forums were closed or made inaccessible in 2007."
As well as China, Cuba and North Korea, the list highlighted 12 other countries where Internet freedoms are restricted: Belarus, Myanmar, Egypt, Ethiopia, Iran, Saudi Arabia, Syria, Tunisia, Turkmenistan, Uzbekistan, Vietnam and Zimbabwe.
A further 11 countries were named as "countries under watch:" Bahrain, Eritrea, Gambia, Jordan, Libya, Malaysia, Sri Lanka, Tajikistan, Thailand, United Arab Emirates and Yemen.
The report also criticized Western companies for cooperating in cyber-repression, citing the case of U.S. company Yahoo! providing information to Chinese censors which resulted in a journalist, Shi Tao, being jailed for 10 years.
"The hunting down of independent thinkers online is all the more effective as several major western companies have colluded with governments in pinpointing 'trouble-makers'," RWB said.
"(Yahoo!) has been responsible for the imprisonment of a total of four Chinese cyber-dissidents. It was apparently willing to 'obey local laws' that forced it to identify Internet users deemed to be dangerous."
Around 5,400 demonstrators had joined the protests by 1300 GMT, including more than 2,000 in China, described by RWB as "the world's biggest prison for cyber-dissidents."
Avatars gathered in a virtual Tiananmen Square carried banners reading "Censorship in China -- faster, bigger, tougher!" and "Free Speech before the Olympic Games!" E-mail to a friend