NOP slide
Because of the popularity of this technique, many vendors of intrusion prevention systems will search for this pattern of no-op machine instructions in an attempt to detect shellcode in use. It is important to note that a NOP-sled does not necessarily contain only traditional no-op machine instructions; any instruction that does not corrupt the machine state to a point where the shellcode will not run can be used in place of the hardware assisted no-op. As a result, it has become common practice for exploit writers to compose the no-op sled with randomly chosen instructions which will have no real effect on the shellcode execution.
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