Thousands of articles have called the December attack against Sony Pictures a wake-up call to industry. Regardless of whether the attacker was the North Korean government, a disgruntled former employee, or a group of random hackers, the attack showed how vulnerable a large organization can be and how devastating the publication of its private correspondence, proprietary data, and intellectual property can be.

But while companies are supposed to learn that they need to improve their security against attack, there’s another equally important but much less discussed lesson here: companies should have an aggressive deletion policy…