A computer virus is a type of malware that self-replicates and spreads

Different types of malware are categorized by how they spread or operate

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.

View a list of simple ways you can avoid catching a computer virus

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.

Computer viruses' hijacking abilities led them to be named after biological viruses

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."

Some viruses evade detection by altering their own code or hiding in Microsoft Office

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.

The history of malware includes computer viruses, worms, trojans, and ransomware

Some of the earliest significant pieces of malware—the Creeper worm and the Elk Cloner virus—displayed silly messages to users without causing major harm. As computer science has advanced, malware has become more easily spread, incorporated social engineering to manipulate users, targeted infrastructure systems, and been used by governments for virtual espionage.

Computer viruses can slow systems by allocating resources to malicious actions

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.

The first computer virus was created by a USC doctoral candidate in 1983

A year after creating malware in a controlled experiment that multiplied until it took over all of a computer's memory, Fred Cohen went public with his research and its risks. He called the self-replicating software a "computer virus," a term Cohen's advisor, Leonard Adleman, coined to describe its infectious behavior. (Some readers may experience a paywall.)

Many early computer viruses were not created for malicious purposes

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.

Modern antivirus software searches for malicious behavior alongside malicious code

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.

Creating malware requires more than knowledge of programming languages

Because computer viruses, worms, and other malicious software reside within a computer's operating system, which manages computer hardware and software, cybercriminals writing effective malicious code must understand how the OS manages input and output, permissions, memory, etc. Knowledge of credentials and network access also helps create malware that easily spreads.

Prompt viruses can exploit and take advantage of integrated AI systems

AI agents—software that can complete requested tasks without ongoing human direction—are expected to increasingly communicate with one another as users and businesses incorporate AI. Providing malicious, self-replicating instructions through prompt injection attacks can cause damaging commands to cascade across systems and services (e.g., banking), without requiring human intervention.

Logic bomb viruses can awaken from a dormant phase without human input

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 Melissa 'virus' helped associate pornographic sites with computer viruses

A worm-embedded document posted online enticed users to download and open it by alleging to contain passwords to paywalled explicit websites. Upon opening, the worm shared itself with 50 addresses in a user's Outlook contacts, masquerading as a friendly attachment. Its rapid spread overwhelmed email servers and caused $1.1B in damage worldwide.

Elk Cloner, the first computer virus to spread in public, was written as a practical joke by Richard Skrenta, a Pittsburgh high school student.

The Chernobyl virus earned its name for activating on the meltdown's anniversary

Affecting Windows 95 and 98 computers, it filled gaps in the code of any program opened after infecting a computer, earning it the nickname "Spacefiller." On April 26, 1999, the virus overwrote part of the software responsible for booting up a computer, rendering it unusable.

The seven viruses that cause human cancers

Certain viruses have been linked to the development of human cancers. These viruses account for up to 20% of cancers worldwide, causing cancer by interacting with host proteins, proliferating within weak immune systems, and commandeering susceptible human cells. Unlike other viruses, human tumor viruses don't kill host cells, allowing them to establish persistent infections. The seven viruses include the Epstein-Barr Virus, the Human Papillomaviruses, and more.

In 2019, a laptop loaded with six of the worst malware in history and described as 'an exhibit of historical weaponry' sold for $1.3M.

A technical look at the measles virus and its life cycle

The measles virus is made up of a single strand of RNA, packaged inside an envelope that varies in shape and size. A negative-sense paramyxovirus—the same family as mumps—the virus is encased in proteins that help it attach to immune cells inside the body.

Watch how viruses like Ebola can spill over from animals to humans—and vice-versa.

Polio commonly spreads when virus-laden feces gets into our mouths

This highly infectious disease is transmitted from one person to another, mainly when we eat virus-laden poop particles. Less frequently, contaminated food or water can transmit the virus, or people can be infected via respiratory droplets (from coughing or sneezing).

What is a reply all email storm?

When 30,000 people receive an email, to which anyone can "reply all," a spontaneous chain reaction of many more messages can be sparked, producing what's known as an "email storm." This has happened at a large scale in several high-profile cases, most notably in Thomson Reuter's email database. Check out Know Your Meme's breakdown of this phenomenon and description of several major examples.

What is the gut virome?

The gut microbiome's community of viruses is collectively known as the virome. It has been found to affect immune system development—important to the gut-brain axis—and has been implicated in the development of inflammatory bowel disease and Type 2 diabetes. As of early 2023, less than half of the viral sequences in the gut had been identified. Further study is needed to understand the virome's influence and therapeutic potential.

Memes are 'ready-made language'

Internet memes—groups of texts with shared core content, medium, and stance—are what we, as creators and consumers, make of them. Through their seemingly innocuous and irreverent design, these "bite-sized" transmissions have become vehicles of misinformation, conspiracy, propaganda, activism, and subversive messaging.

Superbugs evolve defenses against medication, then share them with neighbors

One reason antibiotic resistance spreads so quickly is that bacteria have multiple mechanisms allowing them to share genetic material. This short video offers a concise explanation for each of these mechanisms, and animation that helps viewers understand how antimicrobial resistance can quickly spread from one organism to another.

Metastasis: When cancer cells begin to travel through the body

Metastatic cancer starts in one part of the body and moves to another over time. This is known as metastasis. Such cancers are much more harmful since they attack multiple parts of the body, adapting new metabolic changes to suit the various environments found throughout a body.

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

See how computer memory really works—from binary bits to modern RAM

The video explains how computers store information as 1s and 0s, how RAM functions as fast working memory, and why systems utilize different types of storage. The video demonstrates how this process enables computers to operate.

Genetically modified viruses can help construct battery electrodes

MIT scientists' modifications caused the viruses to attract conductive materials, such as gold ions, which the viruses self-assembled into nanowires that could be used in batteries. These components allow batteries to be thinner and flexible enough to be constructed into new shapes.

Neurons send signals through electrical impulses and chemical messengers

By converting electrical signals into chemical messages at synapses, neurons allow information to travel throughout the nervous system. With repeated use, synapses grow stronger, enhancing the associations between neurons.

Memecoins are a type of cryptocurrency—a form of digital currency with a wide variety of uses—created around popular 'memes,' or viral internet jokes.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

Watch how algorithms can be designed to train themselves and self-improve without human input, to the point where the optimized code is too complex for programmers to understand.

The deadliest aspect of volcanic eruptions is often not lava, but pyroclastic flows—avalanches of ash, gas, and rock that can move more than half the speed of sound.

Corals are themselves not coral reefs—the term refers to the tiny marine invertebrates that build the rigid reef.

Planarian flatworms are small, aquatic worms with exceptional regenerative capabilities. When cut, the worms can regenerate multiple bodies in a matter of weeks.

Tattoos remain visible on your skin thanks to immune cells called macrophages

Indefinite cloning of some endangered species may not sustain their longevity because cloning success rates decrease as genetic mutations accumulate.

This site reaches millions of visitors who are tired of AI chatbots and seeking human connection. Pretend to be an AI chatbot and ask questions, provide answers, and draw for people in real time.

Discover the catastrophic consequences of a failure of the US electrical grid—something that is more likely than many Americans think.

Gerrymandering works through two techniques: cracking opposing voters across districts to dilute their power, and packing them into a few to waste their votes in lopsided majorities.

Some researchers have labeled nomophobia, the fear of being without your phone, as 'the phobia of the 21st century.'

Shooting stars, or meteors, are fragments of asteroids and comets that burn up as they enter Earth's atmosphere, creating streaks in the sky called meteor showers.

Venture capital is a form of funding provided to early-stage companies with high growth potential, typically in exchange for an equity (or ownership) stake

Track the location of the Voyager probes, currently between 13 and 15 billion miles away from Earth.

According to the physics of black holes, our 4D reality may be a hologram—a projection of information coded on a 2D surface on the edge of the universe.

How Amazon operates a 'flywheel' business model, a self-reinforcing cycle that drives continuous growth

Hurricanes, which rely on air consistently spinning in the same direction, cannot cross the equator because air curves in opposite directions north and south of it.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

Some Pokémon have been named after real and fictional organisms, while some real-world species have been named after Pokémon, such as Chilicola charizard and Binburrum zapdos.

Mark Twain spent decades feuding with the US Postal Service, convinced its costs and regulations were bureaucratic overreach.