The last few years game developers more and more are protecting their games with commercial CD Protections. Until now none of these CD Protections have really helped, in some cases it even can work against you as some CD-ROM players can not handle the protection. So we have to wait before game developers get it that it is a waste of effort and money protecting CD's.
Then the music industry hopped the bandwagon and started is selling protected audio CD's. These CD's can be backed up using a variety of methods but usually an easy 1:1 backup is not possible. This is exactly what they want, making it harder to make a backup so that people will buy the original. Only they did not think about the fair use laws which are common in most countries, which make it possible to create a backup for personal use!
As CD's are not 100% indestructible many people want to make a backup of their games. Using the backup to play the game thus saving the original. Especially when it involves children it is VERY handy to have them use a backup. Because of these CD Protections it is getting harder and harder just to make a working backup.
Most protection technologies (like SafeDisc & SecuROM) encrypt the main executable using a key, this key is then added to the disc as a digital signature. A software loader program is added to read the digital signature, extract the key and load/decrypt the main executable.
Keep in mind that in most countries you are legally allowed to make a backup of a CD which you legally own. Some gaming companies won't allow you to make a backup and use the argument that a broken (original) CD will be replaced, but in most cases the costs for replacing it is usually more then buying the game again!
This page contains a list of all known CD, DVD & Media Protections which are currently on the market, how they can be detected and how to by-pass many of them.
For a complete overview of which games use which copy protection checkout the FileForums PC Games Protection List.
There are currently a number of tools which are able to detect which CD Protection is being used on you original CD's, checkout the CD/DVD Utilities page to get them! This page also includes tools to create your own protected data & audio CD's!
= This protection is not used anymore of as "died".