There are many potential sources of viruses, including floppy disks, e-mail messages, shared files, and downloaded documents.
A virus is a program that can be hidden inside another file—it can replicate itself and spread to other files and computers. Different viruses cause different types of damage: one could scan your Microsoft Office Outlook Address Book and send junk mail to all the addresses; another may actually destroy information on your hard drive.
Virtually all viruses try to replicate themselves and infect other files or computers.
Your computer is always at risk from viruses. Shared files, networks, and floppy disks; e-mail attachments; Web-based e-mail; downloads; and malicious Web sites are some of the potential dangers that you might have to navigate. Seemingly innocent documents or attachments can contain deadly viruses.