Computer Virus like a biological virus must have the media to be able to spread, computer virus can spread to various computer / other machines as well as through various media, including:
It is entirely possible for a site deliberately planted a "virus" that will infect the computers that access it.
Floppy disk, storage media R / W
External storage media can be an easy target for the virus to be used as media. Either as a permanent or as a distribution medium. The Media that can perform operations R / W (Read and Write) it is possible to carrying the computer virus and serve as a distribution medium.
Network (LAN, WAN, etc.)
The relationship between multiple computers are directly involved allowing a virus to move away from the exchange / executing the file containing the virus.
Attachment in email, file Transferring
Almost all types of virus spread lately using the email attachment because all internet service users must use email to communicate, these files are accidentally striking / attract attention, and often have a double extension on the file naming.
Freeware, Shareware or Pirated Software
Many computer viruses are deliberately planted in a program that is distributed either free or trial version.
That's some way of spreading a computer virus that generally are frequent. By knowing it, then you can be more careful in working with computers to prevent your computer from spreading of computer viruses into your computer or laptop.