Computer viruses, like their biological counterparts, are species-specific. Computer species are defined by the program-running environment. There are many types and strains of computer virus, the number of which depend on a combination of the popularity of the computer and the ease with which its weaknesses are able to be exploited. Transmission Computer viruses are easily transmitted, as any means of transmitting computer code from one computer to another can pass on infection. Plain text e-mail messages are generally safe because they cannot transmit virus code.
Floppy disks are a common vector for computer viruses.
Any means of transmitting computer code from one computer to another can transmit infection. Software downloaded from bulletin boards or the Internet could contain viruses, although systems operators try not to let viruses infect their systems. Computer networks can help viruses spread rapidly to all computers on the network. Because they are computer programs, they do exhibit very deliberate behaviour. Detailed descriptions of known viruses are available in books, with antivirus programs, or on the Internet.