The importance of audits

Bruce Schenier has a great piece on his blog, which previously appeared in the Wall Street Journal, on the importance of audits. It's a must-read:

Schneier on Security: Audit

... When we think about security, we commonly think about preventive measures: locks to keep burglars out of our homes, bank safes to keep thieves from our money, and airport screeners to keep guns and bombs off airplanes. We might also think of detection and response measures: alarms that go off when burglars pick our locks or dynamite open bank safes, sky marshals on airplanes who respond when a hijacker manages to sneak a gun through airport security. But audit, figuring out who did what after the fact, is often far more important than any of those other three.

Most security against crime comes from audit. Of course we use locks and alarms, but we don't wear bulletproof vests. The police provide for our safety by investigating crimes after the fact and prosecuting the guilty: that's audit....