In preparation for my career as an Air Force intelligence officer, I studied history at the US Air Force Academy. Since then I have enjoyed lectures produced by The Teaching Company, like Famous Romans. One of the lessons I have taken from this course is that defense seldom (if ever) wins wars. I was reminded of this lesson when I read Tom Ptacek's post " The Only Defense Is A Good Defense."
Tom is replying to my post where I said the following:
"I also do not agree [with SANS.edu] that 'knowledge... is the only defense to the growing threat.' The best defense is a strong offense. That means hunting down and prosecuting threats. No amount of defense can sufficient protect any moderately complex enterprise against determined intruders."
Tom disagrees and says that "Firewalls", "IT and Network Security teams", and "Vulnerability Research" have "done the most to improve security over the last 5 years." If we consider the risk equation to be something like "Risk = Threat X Vulnerability X Asset value", we must realize that Tom's points all address the vulnerability side of the equation. Applying countermeasures to the vulnerability aspect of the risk equation leaves the threat component untouched.
When the attacker is allowed freedom of maneuver, the defender will lose. The side with initiative has the superior position, unless the defenses are so unsurmountable that attack is more costly than defense. Let's return to the Famous Romans lecture for a moment. Prior to the rule of the emperor Hadrian, the Roman Empire had pursued an expansionist foreign policy. Rome had lost many battles to its neighbors, but those neighbors essentially remained on the defensive. They feared Rome would invade, conquer, and eliminate them (at worse).
When Hadrian became emperor in 117 AD, he changed Rome's foreign policy. He decided to consolidate the empire's borders. His most famous action was the building of Hadrian's Wall, separating England from Scotland. The wall was the ultimate statement of defense, as is sought to keep barbarians separated from Roman cities like London.
In some respects, this ultimate defensive maneuver was a success; London flourished. However, the building of the wall signalled weakness to Rome's enemies. Instead of being seen as a statement of strength, barbarians interpreted as a sign the Romans would not seek to conquer them. Rome looked weak, not strong. Within a century Rome would come under increasing barbarian attack, and the remaining shell of the western "empire" was formally overthrown in 476 AD.
Now, you might say that defense can prove superior to offense. You might cite trench warfare of the late 19th century, and the horror of World War I. In those cases, it is true that the weapons possessed by each side were so horribly destructive that attacks were fruitless and bloody endeavors. However, the arrival of the tank and over a million US troops changed the equation. Offensive action eventually won WWI for the allies.
A particularly clever historian might say the Cold War was won by defense. Some argue the US out-spent, or had the capability to out-spend, Soviet Russia. That is true. Another factor was President Reagan's plan to build the Strategic Defense Initiative (SDI, or "Star Wars.) SDI changed the security situation for the Soviets. The security paradigm of "mutually assured destruction" held that seeking to wipe out the enemy was a worthless action. Once the enemy detected missile launches, he could reply with his own volley. Both sets of missiles would wipe out each side's weapons, leaving neither with an advantage to leverage in a post-exchange world.
SDI altered this nuclear attack outcome. With SDI deployed, the US could potentially preserve some of its weapons for a second round of attacks. This second round gave the US superiority over its Soviet opponent. Suddenly a nuclear war became "winnable," as insane as that sounds. In this case, then, defense was important, but only to preserve the weapons of offense.
In the final analysis, what makes you feel safer -- a lack of criminals on your street, or iron bars on your windows?