Terrorists to use Twitter?

A report by the US Army says Twitter, the popular microblogging tool, is a weapon that could be used by Al Qaeda to help them carry out attacks.
The full report put together by the 304th Military Infantry Battalion can be viewed here (pdf) and Wired magazine has a good summary of the main points.
In the first half, the report talks about online forums, and the use of GPS functions on mobile phones. In the second half, it considers how these technologies might be used with Twitter for intelligence, surveillance, carrying out attacks and evasion of capture.
The report cites the example of how a group of people protesting at the Republican Convention in September used Twitter to update one another about the progress of the protest and avoid arrest by police.
Some people have already questioned why terrorists would want to use Twitter as it can be easily accessed by anyone on the Web and is a very open form of communication.
While this is usually the case, employing a little more imagination might help us think about how terrorists could use Twitter. Let’s not forget that Twitter is not necessarily open – protecting updates and the use of direct messages is also possible. Yes, Twitter might be able to access them but presumably they aren’t going to monitor them on a regular basis.
What’s more, I assume it wouldn’t be too hard to use code words? When the IRA planned attacks they used mobile phones to coordinate attacks which were inevitably tapped. But they didn’t say: “I’m just planting a bomb” – it was all much more obscure than that. So the seemingly innocent “I have just finished breakfast” might not be a tweet about breakfast at all.
So hypothetically, yes, I suppose terrorists could be using Twitter now or in the future, but it’s important to note that this report doesn’t present any evidence that they actually are.