It has been one month since Sony noticed something was wrong on its PlayStation Network service. Have we learned from the mistakes that led to such an enormous amount of lost data, goodwill, and money? Are we doomed to continue repeating Sony's mistakes?

Let's step back, take a look at the situation as it has played out, and determine what lessons we should take away from this incident.

First, criminals broke into Sony's PlayStation Network systems and went snooping around for data. Unfortunately, the information the criminals were able to access contained people's names, addresses, email addresses, passwords, birth dates, and encrypted credit card numbers. Sony investigated to determine the extent of the breach; a week later, it shut down the network and notified the public.

One week later, Sony announced round two of the compromise, affecting Sony Online Entertainment. This time another production database was dumped, as well as a decommissioned database from 2007 that contained unencrypted credit, debit, and direct debit information.

It didn't stop there. Sony then reported an "attack" in which it claimed a list of sweepstakes winners from 2001 had their names and postal codes stolen. It turned out that no one had to break in to access the data: An insecure Web server contained a world-readable Excel spreadsheet with contestants' PII.

The first lesson for us has to do with messaging, which has not been Sony's strong point. Where people's identities and personal information are concerned, notify them immediately with full details. Sony only waited about a week in the PlayStation incident, but at that point still did not release enough information to assure their customers that their credit cards were safe or to clarify whether their passwords were stored insecurely. The second breach was actually part of the same attack as the first one, but this was also not clearly stated. As it stands, the details of the attacks are still not particularly clear or trustworthy.

Second, we need to track the locations where we store sensitive data, not just to ensure it is encrypted, but to know all of the diverse places we could be storing that data.

We asset-tag our laptops, monitors, and other equipment to know where our physical items are located. It is high time we started tracking where data is located as well. More often than not, data is far more valuable than the "asset" it is stored on.

Third, auditing your public-facing websites for accidental disclosure is good practice. Using version-control tools to ensure the data that is available matches the data you intended to publish can go a long way toward preventing this type of accidental disclosure.

Worst case, some clever Google searches of your Web assets can be an enlightening experience. If you don't do it, then someone else will -- and you might not like the results.

Chester Wisniewski is a senior security adviser at Sophos Canada.