Iranian protesters use it. Chinese dissidents use it. In fact, over 75 million people around the world use Twitter to get their messages out. Why?

Because the micro-blogging service is specifically designed to spread short messages to as many people as possible as quickly as possible--it's also ideal for defeating attempts by totalitarian regimes to block news and information. The company's co-founder and CEO, Evan Williams, recently reiterated the San Francisco firm's support for free speech in countries where governments attempt to censor and limit access to the Internet. At the World Economic Conference in Davos, Williams said Twitter was designed to be part of a network that uses "thousands of applications" that allow users to evade government censors.

"There are even cleverer hacks--that I don't want to talk about widely--to get around the normal blocks," Williams hinted. In fact, programmers continue to work with Twitter on new ways to foil censorship that repressive governments, such as those in China and Iran, attempt to impose.

Currently, Twitter uses a central site to disseminate messages. So like sites such as search engine giant Google (whose site is currently subject to Chinese censorship) direct access to Twitter's pages can be blocked in some countries. However, Williams points out that unlike Google, Twitter doesn't need to directly confront censors because people can still access Twitter indirectly.

Instead of using a computer connected to the Web, for example, many people simply use their cell phones to send text messages (via short message service, or SMS) directly to the service.

"The fact that it can be accessed using SMS in many places complicates censoring," says Whitney McNamara, a consultant and programmer who has built applications for Twitter. "You can't just block a Web site."

While there are several Twitter-specific applications for smart phones, such as Twitterrific and TweetDeck, even the most basic cell phones can be used to send text messages to Twitter. "That's one of the really wonderful and interesting strengths of Twitter," emphasizes McNamara, "it's aimed at the lowest common denominator, SMS."

Nevertheless, it is still possible to block such communications, admits Stowe Boyd, an industry analyst and consultant to social networking sites, "but it's significantly more troublesome." A regime intent on preventing any communication with Twitter would need to censor text messages sent over a cellular service to the specific Twitter code. In some countries where the government has that kind of control over cell providers, such as Iran, that's still possible.

However, "cleverer hacks" are already being used by activists to get around such SMS firewalls. Because the software interface that works with Twitter is openly available, programmers have learned how to write applications that use a number other than the official Twitter SMS code and then automatically redirect messages to Twitter. Of course, once censors discover the new number, they can block that as well.

However, programmers working with Twitter say there are new ways software engineers are developing to overcome even this advanced level of censorship. Engineers say that it may be possible to disguise the true destination of messages by constantly changing the number that appears in traffic destined for Twitter. In such a scenario government spies would be unable to determine simply based on the number that information was being sent out to Twitter.

Ultimately, the only way to stop such programs would be to disable cellular data service across an entire country.
"But most countries don't have that kind of Draconian control" over the cell phone companies, according to Don DeBolt, director of threat research at CA.

In addition, to help activists avoid arrest and government reprisals, programmers are working on more sophisticated ways to protect the identity of those sending news to Twitter.

"There are already ways to anonymize and create a Twitter account in 2 seconds," says David Marcus, director of security research at computer security firm McAfee. However, Marcus and others point out that determined hackers can often suss out a poster's true identity to find out who is sending messages. Consequently, programmers are working to make it even more difficult to trace Twitter users online.

Software such as The Onion Router (aka, Tor) that is used to surf the Web with anonymity is being tailored for such purposes, for example. While such tools could prevent a cyber spy from determining the exact source of a message, a censor could still see what the message contained. In such a case, a repressive government could try to block all messages containing a particular word, much like China blocks searches that use the words "Tiananmen Square." To protect against such scanning, even more elaborate tools can be deployed to encrypt postings and sneak them past censors.

Using a technique reminiscent of the microdots used by spies during the Cold War, secret electronic messages can be hidden within other files, such as digital pictures. Known as steganography, such a technique can be used to hide a message about, say, government troops arresting protesters, within a photo of a dog. To the human eye, the picture would appear unchanged; only a careful analysis of the digital file would reveal that something was concealed within. If a posting to Twitter were hidden within such a file, it would be virtually impossible to detect or block, say experts.

Social Security

Of course, while social networking sites like Twitter and Facebook are increasingly being used to promote free speech, they are also coming under an increasing number of attacks. According to a study by security firm Sophos, there has been a 70 percent increase over the past 12 months in the number of attempts to spread malicious software or malware using these services. Such attacks can not only disrupt service, they can also undermine people's confidence in the validity of any information shared on the service.

In December, for example, self-described Iranian hackers redirected Twitter users to their own web page, and the accounts of famous Twitter users, such as Britney Spears and President Obama, have been hijacked in the past. Even the accounts of Twitter employees themselves have been broken into, revealing confidential corporate documents.

Marcus and DeBolt also warn that the use of fake Web sites to plant malicious programs on the computers of Twitter users is growing. The reason: the 140-character limit of Twitter messages means that people have to use services such as Bit.ly to shorten Internet links they post.

"URL shorteners are risky," underscores Marcus, "because literally you can't see what you're clicking on." He says that more attacks are conducted in this way by hiding real Web addresses behind the shortened code.

At the Davos conference Williams admitted that Twitter remained partially blocked in China and some other countries. But "we hope to enable work-arounds eventually," he said.