A computer virus is a program, piece of code, or programming script which runs without the user's knowledge and performs destructive or otherwise unwanted actions to a computer such as disabling or over-riding security features and making it vulnerable to other attacks. Computer viruses range from annoying and harmless, to extremely dangerous and destructive. Viruses normally replicate themselves by propagating throughout files. Viruses are normally spread by email, through a computer network, via floppy disks, or via the Internet. For a more detailed explaination of the various types of computer viruses, please see our types of viruses article.