Some of the key tools for modern terrorists are new communications methods that have become available in the last decade. These include email, instant messaging (IM), electronic bulletin board systems (BBS), satellite phones, text messaging via cell phones, and VOIP (Voice Over Internet Protocol, or telephone calls made via the Internet). Terrorists have been quick to use all of these, and have been stung, often, when they discovered that intelligence agencies were ahead of them in eavesdropping on these new channels. One by one, the media has presented each of these new technologies as a mighty terrorist weapon. And, time after time, it has turned out that the intel people were able to use terrorist complacency to nail more of the bad guys.
The latest scare comes from VOIP, especially the Skype software. There are over 75 million Skype users worldwide. That many people use Skype, not because it provides encrypted phone calls, but because it is free, and easy to use. Actually, it's only free if you call from computer to computer. If you call to a regular phone, it will cost you a few cents a minute. Still pretty cheap, but it generates enough revenue to make Skype a very profitable product.
At the moment, terrorists can't be sure Skype phone calls are secure from eavesdropping cops. Calls made from computer to computer are encrypted all the way, but those that go to a regular phone, are decrypted as they pass through the phone system. That means these calls can still be scanned by intell agency computers, looking for patterns of certain works that would reveal terrorist communications. But the Skype company has been coy about just how secure their encryption is. Skype uses a 256 bit key, which can only be quickly cracked by the most powerful computers. But that encryption makes it difficult, perhaps impossible, to scan (for key phrases) all computer-to-computer Skype calls. Or does it? It is suspected that Skype has a back door in its encryption that allows police to quickly decrypt Skype phone calls. Skype won't say, either way. But the owners of Skype had previously been involved with developing Kazaa, a system that allowed for massive theft of copyrighted music and videos. Thus the Skype company has a real incentive to stay on the right side of the legal system. While Kazaa turned out to be a money loser (after the record and movie companies came after them, successfully, for abetting copyright infringement), Skype is worth a lot of money. Potentially. If Skype is not declared a threat to someone's national security. So far it has not.
The terrorists, at least some of them, know all this. For the intel agencies, fearful and paranoid terrorists are easier to track down. And if Skype does have a back door, some of the terrorists using it have not been clued in on the risks, and are just feeding more information to the people chasing them.