How do computer viruses spread from one computer system to another?

Computer viruses and related malware spread between systems through several primary methods, often exploiting human behavior or technical vulnerabilities.

Mechanisms of Transmission

• Physical Media: Viruses can transfer to other computers via memory-storage devices, such as USB drives or external hard drives.1
• Network and Online Systems: Once a system is infected, the virus can propagate through computer networks or online platforms.1
• Email and Phishing: Many viruses, particularly worms, spread by automatically forwarding themselves to all contacts in a user's email address book. Attackers often use phishing emails—which may masquerade as legitimate correspondence or contain malicious attachments—to trick users into executing the code.2
• Software Vulnerabilities: Some malware, such as self-propagating worms, exploits specific flaws in operating system protocols or software to gain unauthorized access and replicate across systems.32
• Deceptive Tactics: Malware like Trojan viruses often disguises itself as harmless software or files to encourage users to open or install it, thereby initiating the infection.2

It is essential to maintain updated software and exercise caution with email attachments to mitigate these risks, as the deliberate release of such code is a serious form of cybercrime.32