The Internet is awash with anger, fueled by the disputed election, reports CBS News correspondent Bob Orr.
Gunshots can be heard in a YouTube video, which shows an injured protestor being carried to safety.
On the social networking site Facebook, where Iran's Supreme Leader Ayatollah Khamenei appears to have his own page, there is a scene with demonstrators yelling at police.
But the frontline in this cyber-driven revolt may be Twitter where anonymous protestors and sympathizers are trading short messages.
"This is the first step," one blogger wrote. "We stop Khamenei and Ahmadin."
Another echoed a warning from opposition leader Mousavi, writing: "People will howl for the innocent killed on Monday."
The impact of Twitter has not been lost on the U.S. State Department, which called on the company to defer maintenance to allow the Web site to stay up.
"We promote the right of free expression," said Secretary of State Hillary Clinton. "I wouldn't know a twitter from a tweeter but apparently it is very important."
Computer forensics expert Gary Warner says he has found evidence that opposition forces are actually using Twitter to do more than pass information.
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One can see an actual cyberattack against Iranian government Web sites triggered by a mouse click on a link posted on Twitter.
"Sitting in your living room or your office in the United States you can actually directly involve yourself in the conflict that's going on in Iran," Warner said.
The Iranian government is responding by taking down opposition Web sites and restricting Internet access. Protestors claim some computer equipment has been smashed.
It's impossible to know exactly what is going on in Iran but - accurate or not - information still flows.
"It's exceptionally difficult for a government to lock down communications in this day and age with regard to technology adoption," said CBS News cyberterrorism consultant Paul Kurtz.
Cyber experts say government officials cannot shut down all communications because their supporters use the same tools and they also want to know what opponents are saying. But there are signs tonight Iran's censorship is spreading and becoming more effective.