A computer virus is a type of code that copies itself into other software when a user runs an infected program or file. This action causes damage by altering programs, corrupting files, and compromising digital security. The term was first used in 1984 to describe all types of self-duplicating software and has since been misused as a catch-all for a broad range of malicious software, including adware and spyware. However, computer viruses are distinct from other malware because they require human action to spread.
Hours of research by our editors, distilled into minutes of clarity.
Just as their counterparts infect cells and take control of cellular processes to replicate endlessly, computer viruses cannot replicate on their own and must copy their code into host software before duplicating when the program or file is opened. The term "virus" comes from the Latin word for "venom."
Computer viruses require user interaction to execute a file and spread, whereas worms can self-replicate across systems without human intervention. Ransomware locks systems until a key is provided, spyware tracks and reports user activity to a third party, and trojans disguise various types of malware as legitimate software.
Created by Richard Skrenta, a Pittsburgh high school student, the virus copied itself from an infected floppy disk to Apple II operating systems, then spread to any floppy disks inserted into infected machines. The virus would cause various annoying behaviors that required reboots to resolve, but it would display a poem on the 50th boot of an infected machine.
Computer viruses are often classified by how they spread or which files they infect, with the oldest ones—boot sector viruses—targeting systems that are active when a computer is turned on. Macros—custom codes in office productivity programs authored to automate tasks—spawned their own class of viruses.
Theoretically, computer viruses can remain idle indefinitely while awaiting specific user actions, as instructed by their code. However, logic bombs—embedded code that triggers when specific conditions are met—can automatically execute viruses, such as when a certain date or time is reached.
The software author was among several computer experts in 1988 who suggested that reports on the threat of computer viruses were exaggerated, referring to testimonials of infections and their spread as "urban legends."
Once infected software is run, instructions in the malicious code within the program or file can copy the code to various locations, exacerbating the infection and producing additional symptoms, such as slow performance, altered login credentials, changes to device settings, and system crashes.
Besides those authored in research labs as proofs of concept for self-replicating software, hobbyists would create malware that played music or displayed text and animations that intentionally revealed the infection as a means of showing off, rather than hiding their spread.
Because this type of malware requires human intervention, such as plugging an infected flash drive into a computer or downloading and running an infected file, the chance of infection can be greatly reduced by being cautious about unfamiliar emails, attachments, and links. Keeping systems up to date with the latest security fixes is also crucial.
The first viral infections were identified by comparing the computer code of programs and files with a database of known virus codes, a method known as signature detection. The ongoing creation of new malware made databases continuously outdated, leading to the development of systems that detect patterns consistent with known viral activity.
Since our ancient human relatives began using stone tools to perform tasks, humans have harnessed scientific knowledge and new technologies to expand the boundaries of our understanding of the natural world. From quantum computing and microplastics to artificial intelligence and memory, explore these topics and more with our concise yet informative overviews and expert-curated resources.