Going back to the origin of viruses, it was in 1949 that Mathematician John Von Neumann described self-replicating programs which could resemble computer viruses as they are known today. However, it was not until the 60s that we find the predecessor of current viruses. In that decade, a group of programmers developed a game called Core Wars, which could reproduce every time it was run, and even saturate the memory of other players' computers. The creators of this peculiar game also created the first antivirus, an application named Reeper, which could destroy copies created by Core Wars.

However, it was only in 1983 that one of these programmers announced the existence of Core Wars, which was described the following year in a prestigious scientific magazine: this was actually the starting point of what we call computer viruses today.

At that time, a still young MS-DOS was starting to become the preeminent operating system worldwide. This was a system with great prospects, but still many deficiencies as well, which arose from software developments and the lack of many hardware elements known today. Even like this, this new operating system became the target of a virus in 1966: Brain, a malicious code created in Pakistan which infected boot sectors of disks so that their contents could not be accessed. That year also saw the birth of the first Trojan: an application called PC-Write.

Shortly after, virus writers realized that infecting files could be even more harmful to systems. In 1987, a virus calledSuriv-02 appeared, which infected COM files and opened the door to the infamous viruses Jerusalem or Viernes 13. However, the worst was still to come: 1988 set the date when the "Morris worm" appeared, infecting 6,000 computers.

From that date up to 1995 the types of malicious codes that are known today started being developed: the first macro viruses appeared, polymorphic viruses... Some of these even triggered epidemics, such as MichaelAngelo. However, there was an event that changed the virus scenario worldwide: the massive use of the Internet and e-mail. Little by little, viruses started adapting to this new situation until the appearance, in 1999, of Melissa, the first malicious code to cause a worldwide epidemic, opening a new era for computer viruses.
The Creeper virus was first detected on ARPANET, the forerunner of the Internet, in the early 1970s.[65] Creeper was an experimental self-replicating program written by Bob Thomas at BBN Technologies in 1971.[66] Creeper used the ARPANET to infect DEC PDP-10 computers running the TENEX operating system.[67] Creeper gained access via the ARPANET and copied itself to the remote system where the message, "I'm the creeper, catch me if you can!" was displayed. The Reaper program was created to delete Creeper.[68]
In 1982, a program called "Elk Cloner" was the first personal computer virus to appear "in the wild"—that is, outside the single computer or lab where it was created.[69] Written in 1981 by Richard Skrenta, it attached itself to the Apple DOS 3.3 operating system and spread via floppy disk.[69][70] This virus, created as a practical joke when Skrenta was still in high school, was injected in a game on a floppy disk. On its 50th use the Elk Cloner virus would be activated, infecting the personal computer and displaying a short poem beginning "Elk Cloner: The program with a personality."
In 1984 Fred Cohen from the University of Southern California wrote his paper "Computer Viruses – Theory and Experiments".[71] It was the first paper to explicitly call a self-reproducing program a "virus", a term introduced by Cohen's mentor Leonard Adleman. In 1987, Fred Cohen published a demonstration that there is no algorithm that can perfectly detect all possible viruses.[72] Fred Cohen's theoretical compression virus[73] was an example of a virus which was not malware, but was putatively benevolent. However, antivirus professionals do not accept the concept of benevolent viruses, as any desired function can be implemented without involving a virus (automatic compression, for instance, is available under the Windows operating system at the choice of the user). Any virus will by definition make unauthorised changes to a computer, which is undesirable even if no damage is done or intended. On page one of Dr Solomon's Virus Encyclopaedia, the undesirability of viruses, even those that do nothing but reproduce, is thoroughly explained.[2]
An article that describes "useful virus functionalities" was published by J. B. Gunn under the title "Use of virus functions to provide a virtual APL interpreter under user control" in 1984.[74]
The first IBM PC virus in the wild was a boot sector virus dubbed (c)Brain,[75] created in 1986 by the Farooq Alvi Brothers inLahore, Pakistan, reportedly to deter piracy of the software they had written.[76]
The first virus to specifically target Microsoft Windows, WinVir was discovered in April 1992, two years after the release ofWindows 3.0. The virus did not contain any Windows API calls, instead relying on DOS interrupts. A few years later, in February 1996, Australian hackers from the virus-writing crew Boza created the VLAD virus, which was the first known virus to target Windows 95. In late 1997 the encrypted, memory-resident stealth virus Win32.Cabanas was released—the first known virus that targeted Windows NT (it was also able to infect Windows 3.0 and Windows 9x hosts).[77]

The first academic work on the theory of self-replicating computer programs[60] was done in 1949 by John von Neumann who gave lectures at the University of Illinois about the "Theory and Organization of Complicated Automata". The work of von Neumann was later published as the "Theory of self-reproducing automata". In his essay von Neumann described how a computer program could be designed to reproduce itself.[61] Von Neumann's design for a self-reproducing computer program is considered the world's first computer virus, and he is considered to be the theoretical father of computer virology.[62]
In 1972 Veith Risak, directly building on von Neumann's work on self-replication, published his article "Selbstreproduzierende Automaten mit minimaler Informationsübertragung" (Self-reproducing automata with minimal information exchange).[63] The article describes a fully functional virus written in assembler language for a SIEMENS 4004/35 computer system.
In 1980 Jürgen Kraus wrote his diplom thesis "Selbstreproduktion bei Programmen" (Self-reproduction of programs) at the University of Dortmund.[64] In his work Kraus postulated that computer programs can behave in a way similar to biological viruses.