Computer virus

A computer virus is a bad program.

It needs a host program to live in. It writes its own code into that program. When you run the program, the virus runs first.

Then, the virus makes copies of itself. It puts these copies into other files. This is how it spreads to more computers.

Some viruses just show a message on the screen. Other viruses can break files or make a computer slow. People make them for many reasons. Some want to send a message. Others just want to see if they can.

To stay safe, we use special tools. These tools help find and stop the bad programs. They help keep our computers working well.

A computer virus is a type of malware. Malware is bad software meant to cause harm.

A virus needs a host program to work. It writes its own code into that program. When the program runs, the virus runs first. This lets the virus spread to other files. This way of spreading is called the infection mechanism.

Most viruses have three main parts. The first is the infection mechanism. The second is the trigger. This is like a tiny timer or a rule. It tells the virus when to start its work. The third part is the payload. This is the part that does the actual work. Some payloads are small. They might just show a funny message on your screen. Other payloads are much worse. They can steal private info or break files.

Viruses can also hide. They use stealth to avoid being seen by antivirus software. This software is a tool used to find and stop viruses. In 1982, a virus called Elk Cloner appeared in the wild. It spread using floppy disks. It even showed a short poem on the screen.

Today, people use many tools to keep computers safe.

A computer virus is a type of malware, which is software meant to cause harm. It works by finding a host program to live inside. Once inside, the virus writes its own code into that program. When a person runs the host program, the virus code runs first. This allows the virus to infect other parts of the computer. This process is very much like a biological virus in living things.

Most viruses have three specific parts to help them work. The first is the infection mechanism, which is the way the virus spreads. The second part is the trigger, sometimes called a logic bomb. This is a rule that tells the virus when to start its work. It might wait for a certain date or a specific time. The third part is the payload, which is the actual code that does something. Some payloads are harmless, like a virus hoax that just sends a message. Other payloads can be destructive by stealing data or breaking files.

The idea of self-replicating programs started with math and theory. In 1949, John von Neumann gave lectures about complicated automata. He described how a computer program could be designed to reproduce itself. Later, in 1972, Veith Risak wrote about a working virus for a SIEMENS computer. In 1984, Fred Cohen became the first to explicitly call these programs "viruses." He even showed that no computer program can perfectly detect every single virus.

Many famous viruses have appeared throughout history. In 1971, Bob Thomas wrote the Creeper program for the ARPANET. It would display the message, "I'M THE CREEPER. CATCH ME IF YOU CAN!" In 1982, a student named Richard Skrenta wrote Elk Cloner. This was the first virus seen "in the wild," meaning outside of a lab. It spread through floppy disks on Apple computers. In 1986, the (c)Brain virus became the first for IBM PC computers. It was created in Lahore, Pakistan, by Amjad Farooq Alvi and Basit Farooq Alvi.

Viruses can behave in different ways to stay on a computer. Some are resident viruses that stay in the computer's memory while it is on. Others are non-resident and only scan the disk for targets before they exit. Some viruses, called macro viruses, hide inside documents like Word files. When you open the file, the virus code runs automatically. This is why it is important to be careful with email attachments. Today, an entire industry of antivirus software works to protect users from these threats.

A computer virus is a specific type of malware, which is software designed to cause harm. It functions by modifying other computer programs to insert its own code. This process allows the virus to replicate itself whenever the host program is executed. If this replication is successful, the affected areas are described as being "infected." This term is a metaphor taken from the way biological viruses work in living organisms. Unlike a computer worm, which is an independent program that can run alone, a virus generally requires a host program to function.

To understand how a virus operates, one must look at its three primary components. The first is the infection mechanism, also called the infection vector. This is the method the virus uses to spread, such as a search routine that locates new files on a disk. The second component is the trigger, often referred to as a logic bomb. The trigger is a specific condition that determines when the virus will activate. This condition could be a certain date, a specific time, or even the presence of another program. The final part is the payload. The payload is the actual code that performs the intended activity, which can range from sending a message to stealing confidential information.

Scientists and researchers describe the life cycle of a virus through four distinct phases. The first is the dormant phase, where the virus is idle and takes no action after gaining access to a system. It waits for its trigger to occur. Next is the propagation phase, where the virus begins to multiply and replicate itself. During this stage, it may "morph" or change its code to evade detection by security software. The third is the triggering phase, where the virus moves from being dormant to being active based on its programmed condition. Finally, the execution phase occurs when the payload is released to perform its task, such as crashing a system or displaying a message.

The theoretical foundation for these programs began with the work of John von Neumann. In 1949, he gave lectures at the University of Illinois regarding the "Theory and Organization of Complicated Automata." His work described how a computer program could be designed to reproduce itself. Later, in 1972, Veith Risak published an article describing a functional virus written in assembler language for a SIEMENS 4004/35 system. In 1984, Fred Cohen became the first to explicitly use the term "virus" to describe these self-reproducing programs. Cohen also demonstrated that no algorithm can perfectly detect every possible virus.

History shows several significant milestones in the development of computer viruses. In 1971, Bob Thomas created the Creeper program, an experimental self-replicating program on the ARPANET. Creeper would display the message, "I'M THE CREEPER. CATCH ME IF YOU CAN!" In 1982, Richard Skrenta wrote Elk Cloner, which was the first virus to appear "in the wild" on personal computers. This virus spread via floppy disks to Apple DOS 3.3 systems. In 1986, the (c)Brain virus was created in Lahore, Pakistan, by Amjad Farooq Alvi and Basit Farooq Alvi. It was the first boot sector virus for IBM PC compatibles.

Viruses can reside in different parts of a computer system to achieve their goals. A resident virus installs itself into the operating system and remains in the RAM while the computer is running. It can intercept requests to access files and redirect them to its own replication module. In contrast, a non-resident virus scans the disk for targets and then exits the memory once it is finished. Some viruses, known as macro viruses, are embedded within documents like Microsoft Word files. These are executed automatically when a user opens the document, which is why suspicious email attachments are dangerous.

The impact of these programs is significant and widespread. As of 2013, computer viruses were responsible for causing billions of dollars in economic damage every year. They can target many different systems, including the boot sector of a hard drive or specific operating systems like Windows 95 and Windows NT. Because of these threats, a massive industry of antivirus software has emerged. This industry provides protection for various operating systems to help users defend against these complex digital threats.