General Pointers:

• To know copyguarding techniques means to know 6502 machine/assembly language. It also helps to know the Atari OS so the Atari Technical Users Notes are very helpful.
  

• Any of these techniques can be combined with any others. Multi-techniques can prove very difficult to "crack."
  

• The protection scheme may occur in more than one spot in the program. Sector checks can be made several times during a boot or even between games!