Reader Evan Katz wonders just how safe the data on his Mac is. He writes:
If my computer is lost or stolen--or a person in my office or home just wants to do some digging--can someone log in using their user name (or pull the hard drive and mount it on another Mac) and somehow read my contacts, calendar and email messages by scanning my hard drive?
I'm not sharing any deep dark secrets by telling you that this can be easily done. If someone has physical access to your computer and its hard drive (and time to carry out their nefarious snooping) it's all over. They can simply mount your computer's hard drive as an external storage device, log into their computer with a root account, and then rummage freely through your stuff. Any normal protections that were in place will be defeated by their root powers.
Fortunately Apple provides a way to protect your data in the form of FileVault (which you'll find in the the Security & Privacy system preference in Mountain Lion). When you enable FileVault, your Mac's disk is encrypted. If you have multiple accounts on your Mac, you'll be asked which will be allowed to unlock the drive. This is helpful when Tom, Dick, and Mary all have user accounts on a particular Mac, but you wish to trust only Mary with this kind of access.
Configuring accounts with FileVault access
Once you've approved the accounts, you'll be provided with a recovery key that contains a long string of characters. This is for cases where you've forgotten the password for an account that's authorized to unlock your drive. You can choose to store this key with Apple, so that you can later recover it after answering security questions. Should you have neither the password or recovery key, you're hosed--you can't unlock the drive. Normally it takes a few hours to encrypt a drive.
Of course the weakest link in the chain remains the person sitting in front of the computer. If you leave your Mac on and logged in and then step away from it, another person could sidle in and rifle through your stuff. A weak password could be likewise disastrous. And slapping a sticky note that contains your recovery key to your Mac's monitor is just inviting trouble.