Computer virus

A computer virus is a type of malware that copies itself by changing other computer programs and adding its own code into them. When this happens, the affected programs are said to be "infected," similar to how real viruses work in nature.

Unlike a computer worm, a virus usually needs a host program to work. It places its code inside the host, and when that program runs, the virus runs first, spreading and causing harm. People who create viruses often use tricks to get others to install them, taking advantage of weaknesses in security vulnerabilities to spread their harmful code.

Viruses can be made for many reasons, such as to lock files for profit (like with ransomware), to send a message, or just for fun. They can also aim to disrupt services or explore ideas about cybersecurity and how things change over time. Because of the damage they can cause, many people and companies work hard to create antivirus software to protect operating systems and keep computers safe.

History

The idea of computer programs that can copy themselves started in 1949 when a scientist named John von Neumann gave talks about how a program could reproduce. In the early 1970s, the first known computer program that could copy itself appeared on a network called ARPANET. It displayed a message saying, "I'M THE CREEPER. CATCH ME IF YOU CAN!"

Later, in 1982, a young student named Richard Skrenta created a virus called Elk Cloner for Apple computers. It spread when people shared floppy disks and showed a short poem after the computer was used 50 times. As computers became more common, more of these copying programs appeared, affecting many types of machines and operating systems.

Main article: History of antivirus software

Main articles: History of ransomware and History of malware

Further information: Timeline of computer viruses and worms and Malware research

Design

A computer virus is made up of three main parts: the infection mechanism, the payload, and the trigger. The infection mechanism is how the virus spreads. Some viruses search for files to infect, while others infect files when they are opened or used.

The trigger decides when the virus will activate its payload. This can happen on a certain date, after a specific event, or when certain conditions are met. The payload is the part of the virus that performs its main actions. These actions can include damaging files, stealing information, or displaying messages. Sometimes, the payload might just show a message to many people without causing harm. When the payload runs, it might slow down or freeze the computer.

The life cycle of a virus can be thought of in four phases. In the dormant phase, the virus is present but not doing anything. It waits for a trigger to activate it. In the propagation phase, the virus starts to make copies of itself and spread to other files or programs. In the triggering phase, the virus becomes active because of a specific event. Finally, in the execution phase, the virus carries out its main actions, which could range from deleting files to showing messages on the screen.

Targets and replication

Computer viruses can affect many parts of a computer or its software. Some viruses live in programs you can run, like files ending in .EXE or .COM, while others hide in documents such as Microsoft Word files or PDF files. Some even attach to the very start part of a computer's hard drive, called the boot sector.

Certain viruses stay in your computer's memory all the time, from when you turn it on until you shut it down. These can change how the computer works when you try to use certain files. Other viruses scan your disks for files to change and then disappear after they're done. Some viruses hide in documents or emails that let small programs run automatically when you open them. This is why it's important not to open unexpected files or email attachments from people you don't know. These hidden programs can then affect your computer when you open the file.

Detection

Some viruses try to stay hidden from people by changing how they look. For example, they might keep the same last changed date on files or fit into empty spaces in files without making the files bigger. However, special software designed to find viruses can still spot them by checking for changes in files.

When a virus infects a computer, sometimes it can trick the antivirus software by showing it fake, clean versions of files. To really find these hidden viruses, experts sometimes need to start the computer using a known safe disk and then check the files.

Modern antivirus programs look for special patterns that viruses often use. But some viruses change their code every time they infect a new file, making it harder to spot them. Even with these tricks, antivirus tools keep improving to find and remove these hidden threats.

Effects

Computer viruses can cause problems like making computers stop working, changing important information, using up the computer's energy, costing more money to fix, or taking private details. Even though tools that help protect computers can't find every virus, experts are always working to make these tools better.

Some special programs, called power viruses, can make a computer work too hard and get too hot. Computers are built to handle a certain amount of heat, but these programs might push it too far, which can damage the computer forever. These programs can be harmful, but they are also sometimes used by engineers to test new computers. Other programs that use a lot of computer power are used safely by users to test how fast their computer can go.

Infection vectors

Computers have safety features to stop unauthorized changes, but viruses find weaknesses to spread. They often hide inside programs you use, like files that look like pictures but contain hidden code. When you open them, the hidden code runs.

Viruses spread in different ways. They can hide on devices like flash drives left in public places, hoping someone will use them. Most viruses target computers running Microsoft Windows because many people use it. They spread easily because many users have similar setups. Older viruses used floppy disks to move between computers. Today, viruses can also spread through emails or websites, tricking people into visiting harmful links.

Countermeasures

See also: Malware § Vulnerability to malware, Anti-malware, and Browser security § Browser hardening

Many people use special software called antivirus software to help protect their computers. This software can find and remove harmful programs when someone tries to download or open them. It’s important to keep this software updated because new harmful programs are created all the time.

To stay safe, it’s also a good idea to update your computer regularly, be careful when browsing the internet, and only download software from trusted sources. Making copies of your important files can help you recover if something goes wrong.

Popular culture

The idea of a computer virus first appeared in the 1970 short story The Scarred Man by Gregory Benford. It described a program called VIRUS that spreads from one computer to another through phone lines, trying to copy itself onto any computer it reaches. This story was based on a real program Gregory Benford had created years earlier.

The idea appeared again in books and movies during the 1970s and 1980s. In 2016, a special collection called The Malware Museum of Art was created by Jussi Parikka. It lets people safely see how computer viruses worked on old home computers from the 1980s and 1990s. The collection is hosted at The Internet Archive and was put together by Mikko Hyppönen from Helsinki, Finland.

Other malware

Main article: Malware

Sometimes people use the word "virus" to talk about many kinds of harmful software on computers. This software is called malware and includes things like computer "worms", ransomware, spyware, adware, trojan horses, and keyloggers. Most harmful software today is usually a type of program called a trojan horse or a worm, not a virus.

A real computer virus was named this way in 1985 by Fred Cohen. What makes a virus special is that it can copy itself by changing other programs on your computer without you knowing. This is like how a real virus copies itself inside living cells. Some viruses might try to do bad things, like taking up space on your computer, stealing private information, or showing strange messages. But not all viruses try to hurt your computer right away—the main thing they all do is copy themselves into other programs without permission.