The most simple computer viruses are composed of two essential parts sufficient to ensure the replication. A search routine, which is to search for files suitable to be infected by the virus and check that they do not already contain a copy, to avoid repeated infection of the same file.
A routine of infection, with the task of copying the viral code within each selected file from the search routine because it runs every time the infected file is opened, in a transparent way with respect to the user. Many viruses are designed to execute code extraneously for the purposes of replication and thus contain two other elements:
The activation routine, which contains the criteria according to which the virus decides whether or not to attack (eg, a date, or the attainment of a certain number of infected files). The payload, a sequence of instructions typically harmful to the host system, such as the deletion of certain files or displaying messages on the screen.
The virus can be encrypted and may change algorithm and/or key each time they are run, so they can contain three elements: a decryption routine, which contains the instructions to crack the code of the virus. an encryption routine, usually encrypted itself, which contains the procedure to encrypt each copy of the virus. A routine of mutation, which is responsible to modify the encryption and decryption routines for each new copy of the virus, which can be removed by Anti Virus Support Sydney.
Today, the x86 architecture is widely used – a typical representative of the CISC class – internally actually a RISC architecture, which decomposes the complex instructions provided in simple, RISC -like μ — code.
Another type of processor designs involves the use of the VLIW. There are several instructions that are summarized in one word. This is defined from the beginning, on which unit which instruction is running as shown by Anti Virus Support Sydney
How computer viruses spread
What distinguishes the computer viruses from computer worms is the mode of replication and dissemination: a virus is a fragment of code that can not be performed separately from a host program, while a worm is a program in itself. In addition, some worms exploit security vulnerabilities to spread, and therefore do not depend on fooling you to get it to perform.
Before the widespread use of Internet the prevailing means of dissemination of the virus from one machine to another was the exchange of floppy disks containing infected files or a boot sector virus. The preferred vehicle of infection is instead represented today by e-mail communication and peer to peer networks (eg, eMule).