If you own or use a computer, you are vulnerable to malware. Computer viruses are deployed every day in an attempt to wreak havoc, whether it be by stealing your personal passwords, or as weapons of international sabotage.

Theories for self-replicating programs are first developed.

Apple Viruses 1, 2, and 3 are some of the first viruses “in the wild,“ or in the public domain. Found on the Apple II operating system, the viruses spread through Texas A&M via pirated computer games.

Fred Cohen, while working on his dissertation, formally defines a computer virus as “a computer program that can affect other computer programs by modifying them in such a way as to include a (possibly evolved) copy of itself.“

Two programmers named Basit and Amjad replace the executable code in the boot sector of a floppy disk with their own code designed to infect each 360kb floppy accessed on any drive. Infected floppies had “© Brain“ for a volume label.

The Lehigh virus, one of the first file viruses, infects command.com files.

One of the most common viruses, Jerusalem, is unleashed. Activated every Friday the 13th, the virus affects both .exe and .com files and deletes any programs run on that day.

MacMag and the Scores virus cause the first major Macintosh outbreaks.

Symantec launches Norton AntiVirus, one of the first antivirus programs developed by a large company.

Tequila is the first widespread polymorphic virus found in the wild. Polymorphic viruses make detection difficult for virus scanners by changing their appearance with each new infection.

1300 viruses are in existence, an increase of 420% from December of 1990.

The Dark Avenger Mutation Engine (DAME) is created. It is a toolkit that turns ordinary viruses into polymorphic viruses. The Virus Creation Laboratory (VCL) is also made available. It is the first actual virus creation kit.

Good Times email hoax tears through the computer community. The hoax warns of a malicious virus that will erase an entire hard drive just by opening an email with the subject line “Good Times.“ Though disproved, the hoax resurfaces every six to twelve months.

Word Concept becomes one of the most prevalent viruses in the mid-1990s. It is spread through Microsoft Word documents.

Baza, Laroux (a macro virus), and Staog viruses are the first to infect Windows95 files, Excel, and Linux respectively.

Currently harmless and yet to be found in the wild, StrangeBrew is the first virus to infect Java files. The virus modifies CLASS files to contain a copy of itself within the middle of the file's code and to begin execution from the virus section.

The Chernobyl virus spreads quickly via .exe files. As the notoriety attached to its name would suggest, the virus is quite destructive, attacking not only files but also a certain chip within infected computers.

Two California teenagers infiltrate and take control of more than 500 military, government, and private sector computer systems.

The Melissa virus, W97M/Melissa, executes a macro in a document attached to an email, which forwards the document to 50 people in the user's Outlook address book. The virus also infects other Word documents and subsequently mails them out as attachments. Melissa spread faster than any previous virus, infecting an estimated 1 million PCs.

Bubble Boy is the first worm that does not depend on the recipient opening an attachment in order for infection to occur. As soon as the user opens the email, Bubble Boy sets to work.

Tristate is the first multi-program macro virus; it infects Word, Excel, and PowerPoint files.

The Love Bug, also known as the ILOVEYOU virus, sends itself out via Outlook, much like Melissa. The virus comes as a VBS attachment and deletes files, including MP3, MP2, and .JPG. It also sends usernames and passwords to the virus's author.

W97M.Resume.A, a new variation of the Melissa virus, is determined to be in the wild. The “resume“ virus acts much like Melissa, using a Word macro to infect Outlook and spread itself.

The “Stages“ virus, disguised as a joke email about the stages of life, spreads across the Internet. Unlike most previous viruses, Stages is hidden in an attachment with a false “.txt“ extension, making it easier to lure recipients into opening it. Until now, it has generally been safe to assume that text files are safe.

“Distributed denial-of-service“ attacks by hackers knock Yahoo, eBay, Amazon, and other high profile web sites offline for several hours.

Shortly after the September 11th attacks, the Nimda virus infects hundreds of thousands of computers in the world. The virus is one of the most sophisticated to date with as many as five different methods of replicating and infecting systems.

The “Anna Kournikova“ virus, which mails itself to persons listed in the victim's Microsoft Outlook address book, worries analysts who believe the relatively harmless virus was written with a “tool kit“ that would allow even the most inexperienced programmers to create viruses.

Worms increase in prevalence with Sircam, CodeRed, and BadTrans creating the most problems. Sircam spreads personal documents over the Internet through email.

CodeRed attacks vulnerable webpages, and was expected to eventually reroute its attack to the White House homepage. It infected approximately 359,000 hosts in the first twelve hours. BadTrans is designed to capture passwords and credit card information.

Author of the Melissa virus, David L. Smith, is sentenced to 20 months in federal prison. The LFM-926 virus appears in early January, displaying the message “Loading.Flash.Movie“ as it infects Shockwave Flash (.swf) files.

Celebrity named viruses continue with the “Shakira,“ “Britney Spears,“ and “Jennifer Lopez“ viruses emerging.

The Klez worm, an example of the increasing trend of worms that spread through email, overwrites files (its payload fills files with zeroes), creates hidden copies of the originals, and attempts to disable common anti-virus products. The Bugbear worm also makes it first appearance in September. It is a complex worm with many methods of infecting systems.

In January the relatively benign “Slammer“ (Sapphire) worm becomes the fastest spreading worm to date, infecting 75,000 computers in approximately ten minutes, doubling its numbers every 8.5 seconds in its first minute of infection.

The Sobig worm becomes one of the first to join the spam community. Infected computer systems have the potential to become spam relay points and spamming techniques are used to mass-mail copies of the worm to potential victims.

In January a computer worm, called MyDoom or Novarg, spreads through emails and file-sharing software faster than any previous virus or worm. MyDoom entices email recipients to open an attachment that allows hackers to access the hard drive of the infected computer. The intended goal is a “denial of service attack“ on the SCO Group, a company that is suing various groups for using an open-source version of its Unix programming language. SCO offers a $250,000 reward to anyone giving information that leads to the arrest and conviction of the people who wrote the worm.

An estimated one million computers running Windows are affected by the fast-spreading Sasser computer worm in May. Victims include businesses, such as British Airways, banks, and government offices, including Britain's Coast Guard. The worm does not cause irreparable harm to computers or data, but it does slow computers and cause some to quit or reboot without explanation. The Sasser worm is different than other viruses in that users do not have to open a file attachment to be affected by it. Instead, the worm seeks out computers with a security flaw and then sabotages them. An 18-year-old German high school student confessed to creating the worm. He's suspected of releasing another version of the virus.

March saw the world's first cell phone virus: Commwarrior-A. The virus probably originated in Russia, and it spread via text message. In the final analysis, Commwarrior-A only infected 60 phones, but it raised the specter of many more-and more effective-cell phone viruses.

First discovered in November, the Conficker virus is thought to be the largest computer worm since Slammer of 2003. It's estimated that the worm infected somewhere between nine and 15 million server systems worldwide, including servers in the French Navy, the UK Ministry of Defense, the Norwegian Police, and other large government organizations. Since its discovery, at least five variants of the virus have been released. Authorities think that the authors of Conficker may be releasing these variants to keep up with efforts to kill the virus.

Discovered in June, Stuxnet is a computer worm targeting Siemens industrial software through Microsoft Windows. It is the first worm that corrupts industrial equipment. Stuxnet is also the first worm to include a PCL (programmable logic controller), software designed to hide its existence and progress. In August, security software company Symantec states that 60% of the computers infected with Stuxnet are in Iran. In November, Siemens announces that the worm has not caused any damage to customers. However, the Iran nuclear program is damaged by Stuxnet. Iran uses embargoed Siemens equipment for its nuclear program. A Russian computer company, Kaspersky Lab concludes that Stuxnet is the kind of sophisticated attack that could only be conducted with the full support of a nation.

Flame, a malware that attacks computers using Microsoft Windows, is discovered. A report, released on May 28 by Budapest University's CrySyS Lab, states that "arguably, it is the most complex malware ever found." Flame is capable of recording Skype conversations, audio, keyboard activity, network traffic and screenshots. It is spread over a local network or USB stick. Flame also has a kill command, wiping out all traces of it from the computer.

On June 1, an article in The New York Times states that Stuxnet is part an intelligence operation by the U.S. and Israel called "Operation Olympic Games." Started during George W. Bush's presidency, the operation has expanded under President Obama.

In June, the U.S. Justice Department announced that an international, cooperative effort dubbed Operation Tovar succeeded in gaining control of the GameOver Zeus (GOZ) botnet (a linked network of compromised computers), which had emerged in 2011. Up to 1 million Microsoft Windows computers were infected and the malware was mostly used to access banking credentials in order to illegally withdraw funds.

The GOZ malware was also used in the first example of "ransomware": Cryptolocker, which encrypts personal files and then demands payment in exchange for a key, or secret code, to unlock the files. According to the FBI, there were more than 121,000 victims in the United States and 234,000 victims worldwide, paying approximately $30 million in ransom between Sept. and Dec. 2013.

In August two security firms, Fox-IT and FireEye, made public an online portal called Decrypt Cryptolocker to provide the half million victims an opportunity to "access free keys designed to unlock systems infected by CryptoLocker."