There are many different types of computer virus around. This article does not detail how you can get rid of annoying viruses but it does explain a few of the different types of viruses that you can come across.
Direct Action virus
The Direct Action only comes into action when a file containing the virus is executed. The payload is delivered and the virus essentially becomes dormant; it takes no other action unless an infected file is executed again. Most viruses do not use the direct action method of reproduction simply because it is not prolific, but viruses of this type have done damage in the past. The Vienna virus, which briefly threatened computers back in 1988, is one such example of a direct action virus.
File Infector virus
The File Infector virus is perhaps the most common type of virus as the File Infector takes root in a host files and then begins its operation when the file is executed. The virus may completely overwrite the file that it infects, or may only replace parts of the file, or may not replace anything but instead re-write the file, so that the virus is executed rather than the program the user intended. Although it's called a “file virus” the definition does not apply to all viruses in all files generally - for example, the macro virus below is not referred to by the file virus. Instead, the definition is usually meant to refer only to viruses which use an executable file format, such as .exe, as their host.
While some viruses spread using just one method, multipartite viruses want it all. A virus of this type may spread in multiple ways and it may take different actions on an infected computer depending on variables, such as the operating system installed or the existence of certain files.
A Resident virus is the name used to define any virus that inserts itself into a system’s memory. It may then take any number of actions and run independently of the file that was originally infected. A Resident virus can be compared to a direct payload virus, which does not insert itself into the system’s memory and therefore, only takes action when an infected file is executed.