Faced with similar unrest, other governments have pulled the plug on Internet communications entirely. Iran's authorities appear to have chosen to begin "bandwidth throttling" instead. By limiting the amount of information that gets through every second, the government can effectively slow down the Internet so that the average Internet user has to wait several minutes to add a post to Twitter or upload an image to Flickr. With reduced bandwidth, Zuckerman says, "it's harder to access Internet content from the outside, and it's really hard to upload content."

Some analysts suggest it is unlikely that Iran's Internet connectivity would ever be turned off completely. "It's one thing to anger a group of protesting rioters," says Andrew Lewman, a member of the team behind Tor--software that routes Internet traffic around government filters anonymously. "It's another to hurt the whole population" by shutting off Internet connection. With around 23 million Internet users in Iran, or about 35 percent of the population, Iran has far more Internet users than its Middle Eastern neighbors.

Lewman says that he's surprised by how little the Iranian government has blocked the Internet in recent days, given the attention that the current political unrest has received. He attributes the continuing flow of information out of Iran to two possibilities: either there are people in the government who want to see it disseminated, or the government is tracking and recording everything that's happened in order to round up the perpetrators later. The government's main focus right now, Lewman says, is most likely dealing with the actual protestors on the streets.

Rob Faris, who contributed to the ONI report, is less optimistic about communication flow in Iran. The government has "ramped up filtering in a big way," he says. Even though Twitter remains accessible--through third party apps that don't access Twitter.com for example--"let's not kid ourselves," Faris says. "Access to Twitter, without all the other things you can do with the web, isn't a good deal." Meanwhile, the other measures Iran has taken have "significantly impacted" the communications infrastructure. "They've gone from a repressive regime to a more repressive regime," Faris says.

Still, Zuckerman believes that the Iranian government will likely crack down on the rioters first, and deal with the bloggers later. He suggests that government agencies may be tracking users via their Internet protocol addresses and planning to follow up with arrests.

But the most difficult question regarding the Web's involvement in the current situation, Zuckerman says, is to what extent these tools are helping to organize actual protests. "This is a legitimate street protest; people are extremely upset about their voting rights," he says. Zuckerman senses that the technology isn't helping opposition supporters as much as are traditional organizing methods like phone calls and word of mouth.

According to Steven Murdoch, a computer security researcher at the University of Cambridge, it's hard to tell how many people are actually involved with Web-based protests inside Iran because what we see outside the country is a "biased" sample. Twitter and Facebook are popular in the United States, but there are likely other social-networking sites geared toward Iranians that we can't monitor as closely. So the extent--and reach--of Web activity in Iran is hard to judge.

But the effect on the global community is clear, says Hal Roberts, also of Harvard's Berkman Center: "The press is driven by [Iran's] Twitter stream."