Blaster (2003)

Estimated Damage: 2 to 10 billion dollars, hundreds of thousands of infected PCs

Blaster and Sobig worms. Blaster, also known as Lovsan or MSBlast, was the first to hit. The virus was detected on August 11 and spread rapidly, peaking in just two days. Transmitted via network and Internet traffic, this worm exploited a vulnerability in Windows 2000 and Windows XP, and when activated, presented the PC user with a menacing dialog box indicating that a system shutdown was imminent.

Hidden in the code of MSBLAST.EXE — the virus’ executable " were these messages: "I just want to say LOVE YOU SAN!!" and "billy gates why do you make this possible? Stop making money and fix your software!!"

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Sobig.F (2003)

Estimated Damage: 5 to 10 billion dollars, over 1 million PCs infected

Sobig worm hit right on the heels of Blaster, making August 2003 a miserable month for corporate and home PC users. The most destructive variant was Sobig.F, which spread so rapidly on August 19 that it set a record (which would later be broken by MyDoom), generating over 1 million copies of itself in its first 24 hours.

The virus infected host computers via innocuously named e-mail attachments such as application.pif and thank_you.pif. When activated, this worm transmitted itself to e-mail addresses discovered on a host of local file types. The end result was massive amounts of Internet traffic.

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Bagle (2004)

Estimated Damage: Tens of millions of dollars…and counting

sophisticated worm, made its debut on January 18, 2004. The malicious
code infected users’ systems via the traditional mechanism — an e-mail
attachment — and then scoured Windows files for e-mail addresses it
could use to replicate itself.

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MyDoom (2004)

Estimated Damage: At its peak, slowed global Internet performance by 10 percent and Web load times by up to 50 percent

For a period of a few hours on January 26, 2004, the MyDoom shockwave could be felt around the world as this worm spread at an unprecedented rate across the Internet via e-mail. The worm, also known as Norvarg, spread itself in a particularly devious manner: It transmitted itself as an attachment in what appeared to be an e-mail error message containing the text "Mail Transaction Failed." Clicking on the attachment spammed the worm to e-mail addresses found in address books. MyDoom also attempted to spread via the shared folders of users’ Kazaa peer-to-peer networking accounts.

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Sasser (2004)

Estimated Damage: Tens of millions of dollars

Sasser began spreading on April 30, 2004, and was destructive enough to shut down the satellite communications for some French news agencies. It also resulted in the cancellation of several Delta airline flights and the shutdown of numerous companies’ systems worldwide.

Unlike most previous worms, Sasser was not transmitted via e-mail and required no user interaction to spread. Instead the worm exploited a security flaw in non-updated Windows 2000 and Windows XP systems. When successfully replicated, the worm would actively scan for other unprotected systems and transmit itself to them. Infected systems experienced repeated crashes and instability.

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