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.
