Seven percent said they had acquired their virus while downloading software from an electronic bulletin board service. Technical Overview Viruses are small software programs. At the very least, to be considered a virus, these programs must be able to replicate themselves. They do this by exploiting computer code already on the host system. The virus can infect, or become resident in, almost any software component, including an application, operating system, system boot code or device driver.
Viruses gain control over their host in various ways.
The following is a summary of some more common virus types, how they function, and how you can fight them. They infect file by attaching themselves to a file, generally an executable file the .EXE and .COM files that control applications and programs. The virus inserts its own code in any part of the file. Provided it changes the host's code, the program execution is misdirected so that it executes the virus code first, rather than the legitimate program. While there are only about 200 different boot sector viruses, they make up 75 percent of all virus infections.