Why does Twitter work inside Iran even after other Internet services have been disrupted? The key feature enabling it to evade government censorship, some observers say, is something that might otherwise be considered Twitter's Achilles' heel.
Unlike Facebook, and most other social networking sites, Twitter users don't need to visit Twitter.com to use the service. In the business world, that's a terrible idea. Twitter has no way to promise potential advertisers that its enormous audience will ever see ads placed on the site.
Instead, Twitter has a completely open architecture that allows users to both send and receive messages on a variety of platforms -- cell phones, Blackberries and, of course, other Web sites. This openness is proving to be particularly effective at avoiding government interference.
"You can connect to Twitter without going through Twitter's front door," said Jonathan Zittrain, a Harvard law school professor who runs Herdict.org, which tracks censorship efforts worldwide. "These services run interference between you and Twitter."
Because nearly all of Iran connects to the Internet through a single government-run provider, TCI, it's relatively easy for the government to control Web access. So far, Iranian officials have not shut down the pipe. But over the weekend, it appeared that Web traffic into and out of Iran was substantially slowed -- perhaps intentionally, through a government "throttling" effort.
Zittrain said Iran also deploys filters to cut off access to Facebook.com and some politically oriented Web sites.
But Twitter keeps right on humming, as evidenced by thousands of messages apparently being sent from inside Iran. Some of them are fakes -- and the importance of Twitter in organizing protests in the country is likely overstated: BusinessWeek.com reported that there are only about 8,600 Twitter users whose profiles indicate they are from Iran, citing the Toronto-based firm Sysomos.
Still Twitter's robustness in the face of hostility is impressive. How does it work?
Twitter users theoretically have an infinite number of channels to view each other's posts and send their own. In fact, you don't even have to be a Twitter member to read along at a site like TwitterFall.com, which continuously streams one 140-character post after another.
That makes filtering Twitter.com a useless tactic for would-be censors.
Those trying to evade Web censorship have long used proxy servers as ad-hoc intermediaries, or relays, to connect to the Internet. A cat-and-mouse game ensues: Governments quickly add such proxy servers to their list of blocked sites, new proxies emerge, they are blocked, and so on.
Zittrain said Twitter is not fundamentally different from the proxy server model.
Alternative sites like TwitterFall.com simply act as a relay. They are harder to shut down, however, because the use of intermediary services is part of every Twitter user's experience. While setting up proxy servers can be a technical hurdle for many Web users, Twitter users do it all the time. If one Twitter service isn't working, switching to another is easy.
In fact, Twitter use doesn't even require an Internet connection. The service can be used with cell phone SMS text messages.
"Twitter is more naturally resistant because it doesn't require any intervention from users. It's much more welcoming of proxies," Zittrain said. "It's just so easy to capture a Twitter stream."
Indeed, the 19-year-old inventors of TwitterFall.com say they had their service up and running in a couple of hours.
Of course, shutting down the entire Internet would cut into Twitter access, but that step is probably too Draconian for Iranian authorities. And cutting off text message service -- as the Iranian government apparently did last weekend, immediately after the election -- would still leave more than 20 million Iranians with Web connections and the ability to find Twitter streams. Zittrain said the Iranian government could try to individually eliminate all the services that relay Twitter messages. But in that case, the mouse would appear to have the upper hand.
"My sense is that the authorities have their hands full," he said. Should Iran turn off access to the top 10 Twitter alternatives, users might have some trouble, Zittrain said. But he thinks a Twitter shutdown would be difficult -- because it really is just as easy to set up a new Twitter feed as it is to shut one down. "The cycles we're looking at are measured in hours, not days or weeks. There is furious improvisation going on."