A program that secretly and maliciously inserts unwanted code into program or data files on a system. It spreads by integrating such code into more files each time an infected program is run.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
A malicious program that integrates its own code into a program or file (referred to as the host file) on a computer system, without the knowledge or consent of the user. Viruses spread by infecting other files on a system each time an infected one is run; in extreme cases, after multiple affected files are run, all susceptible files on a system may be infected.
The addition of unwanted virus code into a targeted file usually causes some form of damage to it, leading to instability or total malfunction.
Viruses were once the most common type of malicious program and there are literally hundreds of thousands of viruses in the wild. These viruses are designed to attack various targets on the computer, including:
- Executable or data files, such as applications, games and documents (a file virus)
- The separate, critical boot sector of an operating system, which holds instructions for starting the computer (a boot virus)
- The separate macro scripts used in programs to perform automated functions (a macro virus)
And much more.
A virus almost always arrives on a computer system as an executable file, most popularly as an e-mail attachment. Some viruses are spread as part of a Trojan's payload. Other common ways viruses are spread are through removable media such as floppy disks, CDs or USB thumb drives.