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[1] Encryption is the most common method to hide code. With encryption, the main body of the code (also called its payload) is encrypted and will appear meaningless. For the code to function as before, a decryption function is added to the code. When the code is executed, this function reads the payload and decrypts it before executing it in turn.
This differs from polymorphic code, where the polymorphic engine can not rewrite its own code. Metamorphic code is used by some viruses when they are about to infect new files, and the result is that the next generation will never look like current generation. The mutated code will do exactly the same thing (under the interpretation used), but
On a single-step or immediate-execution calculator, the user presses a key for each operation, calculating all the intermediate results, before the final value is shown. [1] [2] [3] On an expression or formula calculator, one types in an expression and then presses a key, such as "=" or "Enter", to evaluate the expression.
Interest in polymorphic type systems developed significantly in the 1990s, with practical implementations beginning to appear by the end of the decade. Ad hoc polymorphism and parametric polymorphism were originally described in Christopher Strachey's Fundamental Concepts in Programming Languages, [5] where they are listed as "the two main classes" of polymorphism.
It states that two instances of similar code do not require refactoring, but when similar code is used three times, it should be extracted into a new procedure. The rule was popularised by Martin Fowler in Refactoring [1] and attributed to Don Roberts. Duplication is considered a bad practice in programming because it makes the code harder to ...
The first known virus using oligomorphic code was the Whale DOS virus, identified in 1990, which chose from a few dozen distinct decryptors. The first Windows 95 virus using oligomorphic code was the Memorial virus, which could generate 96 distinct decryptor patterns. Another example is the Russian virus family WordSwap. [1]
MEP strength consists in the ability to encode multiple solutions, of a problem, in the same chromosome. In this way, one can explore larger zones of the search space. For most of the problems this advantage comes with no running-time penalty compared with genetic programming variants encoding a single solution in a chromosome. [1] [2] [3]
The use of templates as a metaprogramming technique requires two distinct operations: a template must be defined, and a defined template must be instantiated.The generic form of the generated source code is described in the template definition, and when the template is instantiated, the generic form in the template is used to generate a specific set of source code.