decoy (and the warhead itself) appears the same and is therefore targeted and treated exactly like the "real" warhead, the targeting system simply does not know what is the real threat and what is a decoy due to the mass amount of differing information. This creates a similar situation as the result of the replica decoy, increasing the chance that the real warhead passes through the system and strikes the target. Decoys using antisimulation This type of decoy is perhaps the most difficult and subversive for a missile defense system to determine. Instead of taking advantage of the missile defense system's targeting, this type of decoy intends to fool the operation of the system itself. Rather than using sheer quantity to overrun the targeting system, an anti-simulation decoy disguises the actual warhead as a decoy, and a decoy as the actual warhead. This system of "anti-simulation" allows the attacking warhead to, in some cases, take advantage of the "bulk-filtering" of certain missile defense systems, in which objects with characteristics of the warhead poorly matching those expected by the defense are either not observed because of sensor filters, or observed very briefly and immediately rejected without the need for a detailed examination. The actual warhead may simply pass by undetected, or rejected as a threat. Cooled shrouds Another common countermeasure used to fool missile defense systems are the implementation of cooled shrouds surrounding attacking missiles. This method covers the entire missile in a steel containment filled with liquid oxygen, nitrogen, or other sub-zero coolants that prevent the missile from being easily detected. Because many missile defense systems use infrared sensors to detect the heat traces of incoming missiles, this capsule of extremely cold liquid either renders the incoming missile entirely invisible to detection or reduces the system's ability to detect the incoming missile fast enough. Other types of infrared stealth Another commonly applied countermeasure to missile defense is the application of various low-emissivity coatings. Similar to cooled shrouds, these warheads are fully coated with infrared reflective or resistant coatings that allow similar resistance to infrared detection that cooled shrouds do. Because the most effective coating discovered so far is gold, though, this method is often overstepped by cooled shrouds. Biological/chemical weapons This is perhaps the most extreme approach to countering missile defense systems that are designed to destroy ICBMs and other forms of nuclear weaponry. Rather than using many missiles equipped