"..The anonymous developers of the decryption program that removes DVD copy protection had an easy time doing it, thanks to a gaffe by a software developer and the surprising weakness of the encryption technology.

Essentially, the two European hackers who developed the DeCSS utility that copies a DVD movie disc were able to break the code because one of the product's licensees inadvertently neglected to encrypt the decryption key.

Breaking DVD's encryption was considered extremely difficult, but once the first key was discovered, the rest fell with ease, since the crackers were able to use their original, valid key as a launch point to find more valid decryption keys..."