CRITERIA FOR VIRUS

There are several things that must be met in a program, so that he can be categorized as a virus, namely:  
1. Ability to obtain information 
 In general, a virus requires a list of the names of existing files in a directory. So that he can get a list of files that can he transmitted. For example, the macro virus will infect all files in MS Word, will find a list of extensions *. doc. This is where the ability to gather the information necessary for the virus to create a data / list all files, then sort them by looking for files that bias infected. Normally this data is created when the file is infected / infected with a virus or self virus program files opened by the user. The virus will immediately collect the data and put it (usually) in RAM, so if all the computers shut down all data will be lost. But these data will be created again each time the virus activated. Normally this data is also stored as hidden files by virus. 
2. The ability to check a program  
A virus must also be biased to check a file is infected, for example, he served infect program extensions *. doc, then he should check whether the document files have been infected or not, because if it is, will be useless infect again. This is very useful to enhance the ability of a virus in terms of speed of infecting a file / program. Commonly done by the virus are having / member sign in the file / program that is infected, making it easy to be recognized by the virus. Examples of such labeling is to provide a unique bytes in every infected file.  
3. Ability to multiply  
The core of the virus is the ability to reproduce itself by infecting other files. A virus has found a potential victim if he will recognize to investigate. If not infected then the virus will begin transmission action by writing the byte identifiers on the file, and so on my copy / write the object code of the virus in the target file. Some common ways that done by the virus to infect / reproduce itself are: 
 a. Infected files to be deleted or renamed, then created a file containing the virus program itself using the original file name.  
b. Virus program already in execution / loads into memory will directly infect other files by riding all existing files. 
 4. Their ability to manipulate  
Owned a routine will be executed after virus virus infecting a file. contents of this routine can range from harmless to doing vandalism. This routine is generally used to manipulate files, or popularizing the manufacturer. Routine takes advantage of the ability of an operating system, so have the ability similar to those of the operating system. For example: 
a. Create a picture or message on the monitor  
b. Replacing / changing the label of each file, directory, or labels from the drive on your PC 
c.  To manipulation files infected and damaged files 
d. Disrupting the work printer, and so forth.
5. The ability to hide 
 The ability to hide it should be owned by a virus for all the good work from the beginning to the success of transmission can be accomplished.
Steps that can be done is:  
a. Virus program is stored in coded form and machines combined with other programs that are considered useful by the user.
b. Virus program is put in the boot record or track on the disc are rarely noticed by the computer itself. 
c. Virus program is made as short as possible, and the resulting files are infected do not change size.  
d. The virus does not change the description / inforamasi time a file.