CONFICKER

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Conficker, also known as Downup, Downadup and Kido, is a computer worm targeting the Microsoft Windows operating systemthat was first detected in November 2008. It uses flaws in Windows OS software and dictionary attacks on administrator passwords to propagate while forming a botnet, and has been unusually difficult to counter because of its combined use of many advanced malware techniques. The Conficker worm infected millions of computers including government, business and home computers in over 190 countries, making it the largest known computer worm infection since the 2003 Welchia.
The origin of the name Conficker is thought to be a combination of the English term "configure" and the German pejorative term Ficker (engl. fucker). Microsoft analyst Joshua Phillips gives an alternate interpretation of the name, describing it as a rearrangement of portions of the domain name trafficconverter.biz (with the letter k, not found in the domain name, added as in "trafficker", to avoid a "soft" c sound) which was used by early versions of Conficker to download updates.
                                          SOURCE:https://en.wikipedia.org/wiki/Conficker

ZEUS

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Zeus, ZeuS, or Zbot is a Trojan horse malware package that runs on versions of Microsoft Windows. While it can be used to carry out many malicious and criminal tasks, it is often used to steal banking information by man-in-the-browser keystroke logging and form grabbing. It is also used to install the CryptoLocker ransomware. Zeus is spread mainly through drive-by downloads and phishing schemes. First identified in July 2007 when it was used to steal information from the United States Department of Transportation, it became more widespread in March 2009. In June 2009 security company Prevx discovered that Zeus had compromised over 74,000 FTP accounts on websites of such companies as the Bank of America, NASA, Monster.com, ABC, Oracle, Play.com, Cisco, Amazon, and BusinessWeek. Similarly to Koobface, Zeus has also been used to trick victims of tech support scams into giving the scam artists money through pop-up messages that claim the user has a virus, when in reality they might have no viruses at all. The scammers may use programs such as Command prompt or Event viewer to make the user believe that their computer is infected.
                                                    SOURCE:https://en.wikipedia.org/wiki/Zeus_(malware)

SASSER

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A Windows worm first discovered in 2004, it was created by computer science student Sven Jaschan, who also created the Netsky worm. While the payload itself may be seen as simply annoying (it slows down and crashes the computer, while making it hard to reset without cutting the power), the effects were incredibly disruptive, with millions of computers being infected, and important, critical infrastructure affected. The worm took advantage of a buffer overflow vulnerability in Local Security Authority Subsystem Service (LSASS), which controls the security policy of local accounts causing crashes to the computer. It will also use the system resources to propagate itself to other machines through the Internet and infect others automatically.
                              SOURCE:http://www.hongkiat.com/blog/famous-malicious-computer-viruses/

MELISSA

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Around March 26, 1999 Melissa was put in the wild by David L. Smith of Aberdeen Township, New Jersey. (The virus itself was credited to Kwyjibo, who was shown to be macrovirus writers VicodinES and ALT-F11 by comparing MS Word documents with the same globally unique identifier—this method was also used to trace the virus back to Smith.) On December 10, 1999 Smith pleaded guilty and was sentenced to 10 years, serving 20 months, and was fined US $5,000.^[3] The arrest was the result of a collaborative effort involving (amongst others) the FBI, the New Jersey State Police, Monmouth Internet and a Swedish computer scientist. David L. Smith was accused of causing $80 million worth of damages by disrupting personal computers and computer networks in business and government
                                          SOURCE:https://en.wikipedia.org/wiki/Melissa_(computer_virus)

CODE RED

                                                                                                                     

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         Code Red was a computer worm observed on the Internet on July 15, 2001. It attacked computers running Microsoft's IIS web server.

The Code Red worm was first discovered and researched by eEye Digital Security employees Marc Maiffret and Ryan Permeh, the Code Red worm exploited a vulnerability discovered by Riley Hassell. They named it "Code Red" because Code Red Mountain Dewwas what they were drinking at the time.                                                             Although the worm had been released on July 13, the largest group of infected computers was seen on July 19, 2001. On this day, the number of infected hosts reached 359,000.

SOURCE:https://en.wikipedia.org/wiki/Code_Red_(computer_worm)

I LOVE YOU VIRUS

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ILOVEYOU, sometimes referred to as Love Bug or Love Letter, was a computer worm that attacked tens of millions of Windowspersonal computers on and after 5 May 2000^[1] local time in the Philippines when it started spreading as an email message with the subject line "ILOVEYOU" and the attachment "LOVE-LETTER-FOR-YOU.txt.vbs". The latter file extension (in this case, 'VBS' – a type of interpreted file) was most often hidden by default on Windows computers of the time, leading unwitting users to think it was a normal text file. Opening the attachment activated the Visual Basic script. The worm did damage on the local machine, overwriting random types of files (including Office files, image files, and audio files; however after overwriting MP3 files the virus would hide the file), and sent a copy of itself to all addresses in the Windows Address Book used by Microsoft Outlook. In contrast, the Melissa virusonly sent copies to the first 500 contacts. This made it spread much faster than any other previous email worm.
 SOURCE:https://en.wikipedia.org/wiki/ILOVEYOU
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                                                     https://en.wikipedia.org/wiki/ILOVEYOUhttps://en.wikipedia.org/wiki/ILOVEYOU

What is a VIRUS?

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A computer virus is a type of malicious software program ("malware") that, when executed, replicates itself by modifying other computer programs and inserting its own code.Infected computer programs can include as well, data files, or the "boot" sector of the hard drive. When this replication succeeds, the affected areas are then said to be "infected" with a computer virus.

Computer viruses currently cause billions of dollars' worth of economic damage each year, due to causing system failure, wasting computer resources, corrupting data, increasing maintenance costs, etc. In response, free, open-source antivirus tools have been developed, and an industry of antivirus software has cropped up, selling or freely distributing virus protection to users of various operating systems.

Source: https://en.wikipedia.org/wiki/Computer_virus