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The 10 Most Destructive PC Viruses Of All Time

Computer viruses are like real-life viruses: When they're flying around infecting every PC (or person) in sight, they're scary. But after the fact...well, they're rather interesting, albeit in a gory kind of way. With this in mind, we shamelessly present, in chronological order, the 10 most destructive viruses of all time.

20 Years Of PC Viruses


 A Brief History Of Viral Time

 The 10 Most Destructive Viruses

      •  CIH
•  Blaster

      •  Melissa
•  Sobig.F

      •  ILOVEYOU
•  Bagle

      •  Code Red
•  MyDoom

      •  SQL Slammer
•  Sasser

 Early Days On The Antivirus Front

 What To Do In A Malware Attack

 Virus Image Gallery

 Virus Timeline

CIH (1998)

Estimated Damage: 20 to 80 million dollars worldwide, countless amounts of PC data destroyed

Unleashed from Taiwan in June of 1998, CIH is recognized as one of the most dangerous and destructive viruses ever. The virus infected Windows 95, 98, and ME executable files and was able to remain resident in a PC's memory, where it continued to infect other executables.

What made CIH so dangerous is that, shortly after activated, it would overwrite data on the host PC's hard drive, rendering it inoperable. It was also capable of overwriting the BIOS of the host, preventing boot-up. Because it infected executable files, CIH wound up being distributed by numerous software distributors, including a demo version of an Activision game named Sin.

CIH is also known as the Chernobyl virus because the trigger date of certain strains of the virus coincides with the date of the Chernobyl nuclear reactor accident. The virus is not a serious threat today, thanks to increased awareness and the widespread migration to Windows 2000, XP, and NT, none of which are vulnerable to CIH.

Melissa (1999)

Estimated Damage: 300 to 600 million dollars

On Friday, March 26, 1999, W97M/Melissa became front-page news across the globe. Estimates have indicated that this Word macro script infected 15 to 20 percent of all business PCs. The virus spread so rapidly that Intel, Microsoft, and a number of other companies that used Outlook were forced to shut down their entire e-mail systems in order to contain the damage.

The virus used Microsoft Outlook to e-mail itself to 50 names on a user's contact list. The e-mail message contained the sentence, "Here is that document you asked for...don't show anyone else. ;-)," with an attached Word document. Clicking open the .DOC file -- and thousands of unsuspecting users did so -- allowed the virus to infect the host and repeat the replication. Adding insult to injury, when activated, this virus modified users' Word documents with quotes from the animated TV show "The Simpsons."


Estimated Damage: 10 to 15 billion dollars

Also known as Loveletter and The Love Bug, this was a Visual Basic script with an ingenious and irresistible hook: the promise of love. On May 3, 2000, the ILOVEYOU worm was first detected in Hong Kong. The bug was transmitted via e-mail with the subject line "ILOVEYOU" and an attachment, Love-Letter-For-You.TXT.vbs. Similar to Melissa, the virus mailed itself to all Microsoft Outlook contacts.

Click image to enlarge and to launch image gallery.

The virus also took the liberty of overwriting music files, image files, and others with a copy of itself. More disturbingly, it searched out user IDs and passwords on infected machines and e-mailed them to its author.

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