Answer:
Viruses can enter your computer in any number of ways, such as via an email attachment, during file downloads from the Internet or even upon a visit to a contaminated Web site.Jun 2, 2010
Step-by-step explanation:
Viruses spread when the software or documents they get attached to are transferred from one computer to another using a network, a disk, file sharing methods, or through infected e-mail attachments. Some viruses use different stealth strategies to avoid their detection from anti-virus software.