
	Uh oh...
	Umm, there are a number of copy protection schemes.  Some involve
modifying the physical media, and some involve encryption schemes, &c.
	All of the ones that have existed over the course of computing have
been successful for a time.  I recall, however, near monthly releases of new
ways to "crack" the copy protection scheme of the latest releases.  The fact
is, none of them are completely secure, or anywhere near it.  Some are more or
less difficult to crack, and some have already been cracked.
	I guess what I am saying is that your question is difficult, if not
impossible, to answer.  What exactly do you want to know?  Do you need a good
one for a project you are working on?  How secure must it be?  Are you trying
to crack one that someone else has used?  I can probably make suggestions,
assuming the activity is strictly legal.  (In general, it is a BAD idea,
legally, to tamper with copy protection.  It can also lead to corruption of
files which you necessarily do not have back ups of (being as they are copy
protected,) which can be devestating.)  Do you have absolutely no ideas for
practical applications, and are merely curious?
	Please clear up those questions, and I'll try to help as much as I
can.

	Incidentally, the "Uh oh..." at the top is indicative of the dread
anyone who has watched their friends hacking equipment be carted off feels
when they are asked how to hack.  The area you are broaching is wrought with
dangers, many of which include breaking the law, or at least addressing it
(from one side or the other.)