Over the past year we have been hearing a great deal about cyber warfare. The Pentagon talks about it, and it has also come up in relation to Wikileaks, China and Iran. Which brings up the question: What, exactly, is cyber warfare and how much damage can it really do?

Cyber warfare comes in many forms, and is interesting because the "battleground" is so different from a traditional battleground. Cyber warfare is, essentially, invisible to most people. And the combatants can, in theory, be just about anyone in any part of the world. Even though it is unseen and silent, however, it can still be quite destructive.

Cyber warfare occurs on and through the Internet and other computer networks. The goal is to attack servers on the Internet, the infrastructure of the Internet, or things controlled by machines communicating through networks. It can be as simple as flipping a switch, or as complicated as a grand masters chess game. The best way to understand cyber warfare is to look at some examples.

The simplest example looks more like spying and less like war, but can have big effects. It involves breaking into a computer to steal information. Imagine, for example, that all the plans for the D-day attack in World War II had been stolen. The enemy would have known exactly when, where and how the attack would unfold and could mount its defenses with complete confidence. It would have been a catastrophe.

In the 21st century, just about everything is stored on computers, and in many cases these computers can be accessed from anywhere in the world. If you have the right password, you can log in and start browsing. Cyber soldiers can discover passwords by guessing, by using dictionary attacks, by using social engineering or by accessing back doors. An example of a back door might be a well-known account intended to be used for tech support when the machine is being installed, but then never deleted.

This type of attack brings up another point about cyber warfare — it is not just military entities that are involved. A small group of people might decide to engineer an attack, or a company could try attacking a rival.

Another example would be data interception. Data flows between people and machines on the Internet either through radio waves, wires or optical cables. Data flowing through all three of these media can be intercepted and copied. Ideally, sensitive data would all be encrypted so that this type of attack is pointless. But some things we commonly use, like traditional email, are not encrypted in any way. And sometimes encryption can be broken and the data revealed.

Another cyber warfare tactic was used shortly after Julian Assange of Wikileaks was arrested. Allies of Wikileaks started attacking different entities perceived to be threatening to Wikileaks. Several large financial companies saw their servers fail. These attacks are called Distributed Denial of Service (DDoS) attacks. The idea is to overwhelm Internet servers with so much traffic that they cannot respond to it all. Often DDoS attacks are launched using botnets — collections of thousands or ordinary computers that have been compromised by computer viruses so that other people can control their actions. It is also possible to imagine thousands of people doing the same thing by acting together in a coordinated way.

Speaking of viruses, these computer invaders represent another way to break into an Internet server. If a machine is compromised by a virus or a worm, it would allow someone to copy out data on the machine, or log all the keystrokes typed into the machine (which would include account names and passwords).

One of the most amazing worms seen to date is called Stuxnet. Apparently it is a cyber warfare tool designed to damage certain types of industrial machinery, and is specifically thought to be directed at Iran's ability to enrich uranium. The virus attacks computers that control machines found in factory settings.

The existence of Stuxnet opens up all kinds of possibilities. It is easy to imagine people or viruses that attack internet-connected power grids, drinking water supplies, traffic lights, trucking networks, etc. and bringing parts of society to a standstill. For that matter, it is easy to imagine attacks on anything connected to the Internet. This is one of the unknowns of cyber warfare — it is so new that no one really knows how far it can go. We are sure to find out some of the unexpected possibilities in the not-too-distant future.

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