1. Twitter Is a Tool and Thus Difficult to Censor

Twitter aspires to be something different from social-networking sites like Facebook or MySpace: rather than being a vast self-contained world centered on one Web site, Twitter dreams of being a tool that people can use to communicate with each other from a multitude of locations, like e-mail. You do not have to visit the home site to send a message, or tweet. Tweets can originate from text-messaging on a cellphone or even blogging software. Likewise, tweets can be read remotely, whether as text messages or, say, “status updates” on a friend’s Facebook page.

Image A THOUSAND WORDS Tweets stop at 140 characters. A tweeted photo can have a fuller impact. Credit... SHADISHD173/TWITPIC, via Agence France-Presse — Getty Images

Unlike Facebook, which operates solely as a Web site that can be, in a sense, impounded, shutting down Twitter.com does little to stop the offending Twittering. You’d have to shut down the entire service, which is done occasionally for maintenance.

2. Tweets Are Generally Banal, but Watch Out

“The qualities that make Twitter seem inane and half-baked are what makes it so powerful,” says Jonathan Zittrain, a Harvard law professor who is an expert on the Internet. That is, tweets by their nature seem trivial, with little that is original or menacing. Even Twitter accounts seen as promoting the protest movement in Iran are largely a series of links to photographs hosted on other sites or brief updates on strategy. Each update may not be important. Collectively, however, the tweets can create a personality or environment that reflects the emotions of the moment and helps drive opinion.

3. Buyer Beware

Nothing on Twitter has been verified. While users can learn from experience to trust a certain Twitter account, it is still a matter of trust. And just as Twitter has helped get out first-hand reports from Tehran, it has also spread inaccurate information, perhaps even disinformation. An article published by the Web site True/Slant highlighted some of the biggest errors on Twitter that were quickly repeated and amplified by bloggers: that three million protested in Tehran last weekend (more like a few hundred thousand); that the opposition candidate Mir Hussein Moussavi was under house arrest (he was being watched); that the president of the election monitoring committee declared the election invalid last Saturday (not so).

4. Watch Your Back

Not only is it hard to be sure that what appears on Twitter is accurate, but some Twitterers may even be trying to trick you. Like Rick’s Café, Twitter is thick with discussion of who is really an informant or agent provocateur. One longstanding pro-Moussavi Twitter account, mousavi1388, which has grown to 16,000 followers, recently tweeted, “WARNING: http://www.mirhoseyn.ir/ & http://www.mirhoseyn.com/ are fake, DONT join. ... #IranElection11:02 AM Jun 16th from web.” The implication was that government agents had created those accounts to mislead the public. ABCNews.com announced that Twitter users who said they were repeating (“retweeting”) the posts from its reporter, Jim Sciutto, had been fabricating the material to make Mr. Sciutto seem to be backing the government. “I became an unwitting victim,” he wrote.