This article from this month's Sydney Morning Herald describes the means by which terrorists have used the Internet to communciate and avoid detection, as well as the difficulties that governments face in identifying terrorist activity on the Internet: {C}
The internet has... been a crucial planning tool and conduit for command and control for jihadists planning their attacks. The attacks of September 11, 2001, the Iraqi insurgency, the London bombings and the alleged terrorist plot in Sydney and Melbourne uncovered last year all used the internet to plan and execute operations.
More often than not, terrorists can spread their propaganda, plan their attacks and gather funds without being detected. It's a critical development because intelligence agencies have had considerable success penetrating radical mosques where much of the organising previously took place.
"Unfortunately, it's incredibly difficult for governments to track them down," [Adam] Raisman says. "They set up proxy addresses, virtual servers and use password-protected sites."
Some of the techniques of evasion are disarmingly simple. Rather than send emails, some jihadists simply write and save draft emails, storing them in an account with a password that's known to other members of the cell. Because they are never actually sent, they can't be detected by intelligence agencies.
Raisman points to a recent publication by the al-Fajr group, another communications arm of al-Qaeda and its fellow travellers. He said it contained a very sophisticated manual on internet security, how to avoid hackers, secure personal files and ensure any computer that is captured is of little value to Western authorities....
In testimony to the U.S. Congress earlier this year, [Georgetown University professor Professor Bruce] Hoffman warned the U.S. was "dangerously behind the curve" in dealing with the terrorist presence on the web.