From Technology Review‘s “Terror’s Server“:
For example, research suggests that people with nefarious intent tend to exhibit distinct patterns in their use of e-mails or online forums like chat rooms. Whereas most people establish a wide variety of contacts over time, those engaged in plotting a crime tend to keep in touch only with a very tight circle of people, says William Wallace, an operations researcher at Rensselaer Polytechnic Institute.
This phenomenon is quite predictable. “Very few groups of people communicate repeatedly only among themselves,” says Wallace. “It’s very rare; they don’t trust people outside the group to communicate. When 80 percent of communications is within a regular group, this is where we think we will find the groups who are planning activities that are malicious.” Of course, not all such groups will prove to be malicious; the odd high-school reunion will crop up. But Wallace’s group is developing an algorithm that will narrow down the field of so-called social networks to those that warrant the scrutiny of intelligence officials. The algorithm is scheduled for completion and delivery to intelligence agencies this summer. …