What does Cluster Virus mean?
A cluster virus is a type of virus that ties its own execution to the execution of various software programs. These viruses typically work by changing directory or registry entries so that when someone starts a program, the virus will start as well.
Techopedia explains Cluster Virus
Experts call this type of virus a cluster virus partly because it can load various directory pointers that make it look like every program on a disk is infected with the virus, when in fact, only one copy of the virus exists.
Experienced users can sometimes get around a cluster virus using the checkdisk utility and other elements of the operating system to diagnose and remove the virus. However, less savvy users can end up erasing vital program information through the use of operating system prompts.
One prominent example of a cluster virus is the Dir-2 virus. This is sometimes classified as a "stealth" virus because of some of its natural protections. This virus is commonly attributed to Bulgaria, and attacks various types of executable files.