Experts said the unrest highlighted power of Internet firms -- sometimes wielding more than governments.
Google lists eight reasons on its "YouTube Community Guidelines" page for why it might take down a video. Inciting riots is not among them. But after the White House warned last week that a crude anti-Muslim video had sparked lethal violence in the Middle East, Google acted.
Days later, anger over the 14-minute clip from "The Innocence of Muslims" was still roiling the Islamic world, with access blocked in Egypt, Libya, India, Indonesia and Afghanistan -- keeping it from easy viewing in countries where more than a quarter of the world's 1.6 billion Muslims live.
Legal experts and civil libertarians said it highlighted how Internet companies, most based in the United States, have become global arbiters of free speech, weighing complex issues that traditionally are the province of courts, judges and, occasionally, international treaties.
"Notice that Google has more power over this than either the Egyptian or the U.S. government," said Tim Wu, a Columbia University law professor. "Most free speech today has nothing to do with governments and everything to do with companies."
In temporarily blocking the video in some countries, legal experts say, Google implicitly invoked the concept of "clear and present danger." That's a key exception to the broad First Amendment protections in the United States, where free speech is more jealously guarded than almost anywhere in the world.
The Internet has been a boon to free speech, bringing access to information that governments have long tried to suppress. Google has positioned itself as an ally of such freedoms, as newspapers, book publishers and television stations long have. But because of the immediacy and global reach of Internet companies, they face particular challenges in addressing a variety of legal restrictions, cultural sensitivities and, occasionally, national security concerns.
"Google, YouTube, Facebook, Twitter now play this adjudicatory role on free speech," said Andrew McLaughlin, a former policy official at Google who later worked for the Obama White House as deputy chief technology officer.
Google said it decided to block the video in Egypt and Libya because of the "very sensitive situations there" and not because the White House requested that it review the video. The decision has drawn an uneasy reaction from some. "It's a little bit of censorship and a little bit of diplomacy in a difficult situation," said Jennifer Granick, director of civil liberties for the Stanford Law School Center for Internet and Society.