It was 25 years ago when the first computer virus, the Morris Worm caused an unprecedented havoc by infecting around 6,000 computers. Since then, there have million of computers around the world getting infected by other viruses or worms. In this digital era, internet has become main target for hackers and crackers around the world for it has become the backbone of this modern society. Recently Internet security firm Norton has done a study and have piled up a list of 5 biggest computer viruses of all time.

Let’s have to look to these viruses and the destruction they caused.

MYDOOM (2004)


cv 1 DAMAGES: $38,000,000,000

PCs Infected: 2,000,000

What was it: A worm that spread through email as what appeared to be a bounced message.

How it worked: When the unsuspecting victim opened the email, the malicious code downloaded itself and then pilfered the new victim’s Outlook address book.

How it spread: From there, it spread to the victim’s friends, family and colleagues. It spread faster than any worm seen prior.

SOBIG.F (2003)


cv 2 DAMAGES: $37,100,000,000

PCs Infected: 2,000,000

What was it: A worm that replicates itself, but also is a Trojan, as it disguises itself as something other than malware.

How it worked: Once the user opened the email, it triggered the worm, which then went hunting for addresses.

How it spread: The flood of messages it then sent were capable of succumbing other users’ inboxes or computer systems by the sheer volume of emails. It briefly brought down freight and computer traffic in Washington, D.C. to a halt, grounded Air Canada and slowed down computer systems at many major companies.

I LOVE YOU (2000)


cv 3 DAMAGES: $15,000,000,000

PCs Infected: 500,000

What was it: An innocent looking email attachment labeled “I Love You”.

How it worked: When opened, it unleashed a malicious program that overwrote the users’ image files. It was designed to steal Internet access passwords.

How it spread: The virus emailed itself to the first 50 contacts in the user’s Windows address book.


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CODE RED (2001)


cv 4 DAMAGES: $2,600,000,000

PCs Infected: 1,000,000

What was it: A worm that exploited operating system vulnerability in machines running Windows 2000 and Windows NT.

How it worked: This allowed it to deface and take down some websites, most memorably the website and forced other government agencies to temporarily take down their own public websites as well.

How it spread: The worm spread by randomly selecting 100 IP addresses at a time, scanning the computers for the Microsoft system and then spreading only to those computers.

SLAMMER (2003)


cv 5 DAMAGES: $2,600,000,000

PCs Infected: 1,000,000

What was it: An Internet worm (also called Sapphire) that caused a denial of service on some Internet hosts and dramatically slowed down general Internet traffic.

How it worked: It worked by releasing a deluge of network packets, units of data transmitted over the Internet, bringing the net on many servers to a near screeching halt.

How it spread: As it began spreading throughout the Internet, it doubled in size every 8.5 seconds. It selected IP addresses at random to infect, eventually finding all susceptible hosts. Among its list of victims was Bank of America’s ATMs, a 911 emergency response system in Washington State, Continental Airlines and a nuclear plant in Ohio.


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