Computer virus
Computer virus
A computer virus is a type of malware that, when executed, replicates itself by modifying other computer programs and inserting its own code. Viruses often cause damage to data, system functionality, or network performance. They are one of the oldest and most widely recognized forms of malicious software, distinct from worms or Trojan horses by their need for a host program and user action to spread.
History
The concept of self-replicating programs was first theorized by John von Neumann in the 1940s. The first known computer virus, "Creeper", was created in 1971 on the ARPANET. It displayed the message "I'm the creeper, catch me if you can!" but was not destructive. The "Elk Cloner" virus, written in 1982 for the Apple II, is often cited as the first large-scale virus, spreading via floppy disks. The 1980s and 1990s saw a proliferation of viruses for MS-DOS and Microsoft Windows, including the infamous CIH (1998) and Melissa (1999). Modern viruses often combine with other malware types and are spread via email, USB drives, and drive-by downloads.
Features
- Replication mechanism: Viruses attach to executable files, scripts, or document macros. When the host is run, the virus code executes and looks for new targets.
- Payload: Can range from harmless pranks (e.g., displaying messages) to destructive actions like deleting files, corrupting data, or stealing credentials.
- Stealth techniques: Some viruses hide their presence by intercepting system calls or encrypting parts of their code (polymorphic code).
- Residency: Viruses may be memory-resident, staying active in RAM to infect files as they are opened, or non-resident, executing only when the host runs.
Prevention and mitigation
Anti-virus software uses signature-based detection, heuristic analysis, and behavioral monitoring to identify viruses. Regular software updates, cautious attachment handling, and firewalls reduce infection risk. No system is perfectly immune; the Morris worm (1988) and ILOVEYOU (2000) demonstrated how quickly viruses can spread globally.