Storing credit card information securely and legally is very difficult and should not be attempted. I have no intention of storing credit card data but I\'m dying to figure out
In some situations, encryption keys are stored not on disk but on some hardware device. Either a special encryption server is used to do the encrypt/decrypt or the decrypt is done using a key stored on, say, a hardware dongle. This way, a hacker cannot steal the decrypt keys without stealing the physical device containing them (since the key never leaves the device).
Another method I have seen is to store encrypted data in a database/datacenter that has no direct connection to the outside world (you can't hack what you can't access). An interface server sits between the "secure" part of the network and the "Internet-facing"/"insecure" part of the network as a proxy. Forcing secure traffic to funnel through this security choke point can make it more difficult for an intruder to access the secured data.
Neither of these mean your data is perfectly secure, of course.