Do you know who's in your building at night? Can you positively vouch for all those here-today, gone-tomorrow contract staff who clean and maintain your offices? Physical access is a worryingly simple vector for data-stealing malware, as we'll see in this edition of The Long View...
It's a truism in computer security that all the software in the world won't help you, if you don't have physical security. If you can't stop a Bad Guy walking up to your server in the middle of the night, you can't stop him from stealing your data or injecting malware into your system.
In other words, physical access trumps many software defenses.
Erecting a secure boundary around your server rooms obviously makes sense. Keeping your crown jewels under lock and key is always a good strategy. But what about your PCs? They're usually physically vulnerable to, say, office cleaning staff; and Bad Guys can use some powerful techniques to inject unwanted code into your machines.