Classification of viruses.

Nowadays it's known for about six thousand of the viruses' types, they may be classified according to sphere of operating, way of penetrating into sphere of operating, influence upon the computer system, and peculiarities of the algorithm. According to sphere of operating viruses may by classified as network viruses, file infectors, boot viruses and boot-file viruses. Network viruses are spreading all over the various computer networks, for example all over the internet network or home network of company's network. Viruses copy their selves from one computer to another by means of network connection. File infectors in most cases integrates into executable modules, exactly into files with com and exe add-ins. They also may integrate their selves into files with another add-ins, but after that they lose the ability for multiplying as it's impossible to capture administrating of such files. Boot viruses integrate into boot-sector and operate there; they also may integrate into Master Boot Record. Boot-file viruses may integrate both boots and files and operates there after capturing administration.

According to the way of infection viruses are classified as resident and non-resident. Resident viruses leave in the operating system of your computer its residential part after penetration. The residential part block the operating of the infected files; operating systems refers to infected file and the residential part of the virus blocks this refer and you gat the message on your desktop that file can't be found. Resident viruses keep active until the power off. Non-resident viruses don't injure the memory of the computer and keep active for a very short period of time.

According to intensity of injury viruses may be classified as nonhazardous, hazardous and extremely hazardous. Nonhazardous viruses don't block system operation; they reduce free short-term and HDD memory of the computer. Activity of these viruses usually influences the visual or audio effects. Hazardous viruses may cause serious errors of computer's operating. Extremely hazardous viruses erase software, datum and the information of the boot sector.

Viruses are difficult to classify according to peculiarities of their algorithm because of their great variety. The elemental viruses change the content of the files and boot sectors, the damage they cause is not as dangerous for computer, besides elemental viruses are easy to detect and dispose. Replicate viruses, so called worms, are spread all over the network, detect the IPs of the network's computers and copy themselves to each computer. There're invisible viruses, so called stealth viruses that are hard to detect and dispose as they are simply invisible and their main function is blocking of requests of operating system and replace their body with uninfected sectors of the disk. The most difficult to detect and dispose are the mutant viruses, as they contains coding-decoding algorithm owing to which two copies of the same virus have no single repetitive bytes train.

You may have heard about such type of viruses as Trojan. Trojans are very harmful viruses because they mask as a useful software and injures boot sector and disks' file system; Trojans are able for duplication.