Removable media like CDs and USB drives that have been used on infected systems can spread viruses to other computers. It is important to have reliable antivirus software to protect your computer. Free antivirus programs available online can help prevent diseases from infecting your system before damage occurs. When surfing the internet, most computers become infected within 20 minutes without protection. To avoid viruses, only download files from trustworthy sources and use antivirus software to scan for infections regularly.