Polymorphic viruses.
Polymorphic virus – a tortious program (actually just like the any other virus) that can deal with a number of different types of data, meaning can damage and infect the number of different types of data. Today it's the most dangerous type of the viruses. You want to know why? I'll tell you why. Polymorphic viruses modifies their code in the infected programs so virtuously that two copies of the same virus may be totally different and have nothing in common in a single bit. No wonder this property makes them almost invisible for antivirus programs.
Virus of this type not only codifies its body using different ways of coding, but also contains code of generating coder and decoder. This ability is the distinctive characteristic of polymorphic viruses, because other types of viruses are also able to codify their bodies, but they have an unvarying code of coder and decoder. Unlike these types of viruses polymorphic viruses supplied with selfidentified decoder. You may ask why someone should supply an ordinary virus with such difficult function, and the answer for your question is simple – this function guaranties that you won't be able to analyse and determinate virus' code by means of elementary disassembly even if you have both the source and infected files.
The code of polymorphic virus is codified in that way that code looks like a chaotic and senseless chain of commands. Decoding is performed by means of virus during its operating, other words during contamination of files. Besides, it may not be true that virus will decode itself totally, it may decode itself partially. Virus decodes those pert that are necessary for operating right this moment, and as their work is done virus codifies them and decodes another part of the program. I hope you realise that such ability of the virus makes it a yard one to detect and dispose.
According to what we have learned about polymorphic virus we may summarise that it is entitled to be called the most dangerous virus of all known. Polymorphic viruses are provided with a unique system of codifying and decoding of their own body, and if so they are simply undetectable for antivirus programs. To the program of the virus the empty commands are added, the so called trash, that supplies difficulties of virus' detecting. Sure if there's a virus there should a weapon against it, as we know that viruses are created as marketing mean for pushing up the antivirus program sales. Anyway we should credit for the 'evil genius' whose brilliant mind born this virus, and be grateful to him for he haven't forget to create a panacea from it. So my dear internet and computer users be careful, always use the lust releases of antivirus programs with updating viruses archives. Best wishes)