The Internet enemies list numbers 13: Belarus, China, Cuba, Egypt, Iran, Myanmar, North Korea, Saudi Arabia, Syria, Tunisia, Turkmenistan, Uzbekistan and Vietnam.

These are the countries singled out by the press freedom group Reporters Without Borders as the worst culprits for systematic online censorship, and they were targeted in the group's 24-hour online protest ending at 5 a.m. Wednesday.

"No one should ever be prevented from posting news online or writing a blog," said the Paris-based group, Reporters Sans Frontieres in French, which taps more than 100 journalists who are "keeping us informed."

Worldwide, 61 people, 52 in China, are in prison for posting what the countries claimed was "subversive" content, the reporters' group said in its annual report.

The cyberspace demonstration was advertised in Manhattan -- in Times Square and in Bryant Park -- on truck-transported billboards. As of Tuesday afternoon, 10,000 people had registered their protest, with black holes on the group's Web site gradually disappearing with each click, said Lucie Morillon, the group's spokeswoman in Washington.

The 13 countries "censor and block online content that criticizes them," the organization said in defining its protest. "Multinationals such as Yahoo! cooperate with the Chinese government in filtering the Internet and tracking down cyber-dissidents."

Reporters Without Borders said it obtained a copy of the verdict in the case of Jiang Lijun, sentenced to four years in prison in November 2003 for his online pro-democracy articles in China. Reporters Without Borders said that the search engine company Yahoo! Inc (Nasdaq:YHOO - news). had helped Chinese police identify him.

"It's one thing to turn a blind eye to censorship -- it's another thing to collaborate," Morillon said.

In a statement, Yahoo! said: "We continue to employ rigorous procedural protections under applicable laws in response to government requests for information, maintaining our commitment to user privacy and compliance with the law."

In Cuba, Reporters Without Borders said, the government "ensures that there is no Internet access for its political opponents and independent journalists, for whom reaching news media abroad is an ordeal."

The punishment for writing "a few counterrevolutionary articles" for foreign Web sites can be years in prison, it said.

Reporters Without Borders said it tracks cases of online repression in various ways, including through court cases and reports of arrests by family and friends.

The nonprofit group, founded in 1985 by French journalist Robert Menard, is 70 percent funded by sales of its magazine, Reporters Without Borders For Press Freedom, which includes photos of journalists in jail. About 200,000 copies are printed three times a year.

Nepal, Maldives and Libya have been removed from Reporters Without Borders' annual list of Internet enemies. But there's an addition to the list, Egypt, where it said "many bloggers were harassed and imprisoned this year."