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Top 10 Damaging Computer Viruses

VO: Rebecca Brayton WRITTEN BY: Jonathan Kantor
Be careful what you click on. For this list, we’re taking a look at the most damaging computer viruses, worms, and malware to ever bring down the Internet. Whether they crippled a network or damaged millions of dollars’ worth of equipment, these lines of code are nothing to scoff at. WatchMojo counts down the Top 10 Damaging Computer Viruses. Special thanks to our user SpongeBobSquarePants for suggesting this idea! Check out the voting page at https://www.WatchMojo.comsuggest/Top+10+Damaging+Computer+Viruses.

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Script written by Jonathan Kantor

Top 10 Damaging Computer Viruses

Be careful what you click on. Welcome to and today we’re counting down our picks for the top 10 most damaging computer viruses.

For this list, we’re taking a look at the most damaging computer viruses, worms, and malware to ever bring down the Internet. Whether they crippled a network or damaged millions of dollars’ worth of equipment, these lines of code are nothing to scoff at.

#10: OSX/RSPlug.A Trojan

People who use Apple Computers used to believe they were safe from viruses. Sadly, that belief was debunked when the OSX/RSPlug hit the Internet in 2007. The first virus to target Apple’s OS with the goal of making money, it came in the form of a Trojan horse found in message boards promoting adult content online. If you were foolish enough to click a link in one of these messages indicating your QuickTime was out of date or offering a game download, then you caught the bug! Fortunately, the damage was minimal, but it did expose Apple users to a previously unconsidered danger. And once lost, internet innocence can’t be regained.

#9: Conficker

Back in November 2008, the Conficker worm was released unto the wilds of Windows to steal administrator passwords and create a botnet. Up to 15 million corporate, government and home PCs were infected, making it the single largest computer worm infection in 5 years and resulting in some $9 billion in damages. The worm was difficult to remove due to its multi-pronged attack methodology, but it was eventually defeated. Nobody knows who started the worm, but it is believed to have originated in the Ukraine. If you know who’s responsible, let Microsoft know and they’ll cut you a check for $250,000.

#8: SQL Slammer [aka Sapphire]

Don’t you hate it when your Internet connection slows to a crawl? Back in 2003, that might have been due to the presence of the SQL Slammer or Sapphire worm, which spread so rapidly that 75,000 infections occurred within 10 minutes - causing nearly $1 billion in damages. It was a denial of service attack, which targeted users’ favorite websites, causing them to crash. Though it debuted in 2003, it returned in 2017 to attack legacy servers online that still haven’t patched to defend themselves against the attack. Hey, at this point, they are kind of asking for it.

#7: Stuxnet

Computer viruses are usually more of a nuisance or costly problem than a highly engineered weapon capable of causing real world damage. Stuxnet may have been the very first weapon made entirely out of code and it was used for the specific purpose of taking down Iran’s primary nuclear enrichment facility. Up to 1,000 centrifuges were damaged or destroyed due to the virus’ infection. Iran began recruiting hackers into the Iranian Guard to defend against similar threats, joining the US, China, and other nations in the art of Cyber Warfare. Nobody has claimed responsibility, but the United States and Israel have been pointed to as the likely culprits.

#6: Code Red & Code Red II

When it comes to naming a virus, you might think the security company analyzing it would choose something more interesting than the beverage they were drinking at the time. But nope: a computer worm released in 2001 was named after Mountain Dew Code Red. It went on to wreak havoc and annoy users all over the Net. Infected websites were defaced to read “HELLO! Welcome to! Hacked By Chinese!” It also launched denial of service attacks and targeted the White House’s website. Two weeks later, Code Red II was released to exploit a security hole. Embarrassingly, Microsoft had released a patch for that hole – but hadn’t used it themselves.

#5: Storm Worm

Storm Worm was a backdoor Trojan horse that was released on the Internet back in January 2007 to infect computers running Microsoft Windows OS. Those infected were unlucky enough to have clicked on an email with the subject line “230 dead as storm batters Europe.” The worm infected computers in Europe and the United States and is believed to have originated in Russia. The purpose of the worm was to create a large botnet/zombie network, which may have encompassed up to 10 million computers by September of 2007.

#4: Mydoom

In January 2004, the world was hit with, what was, at the time, the fastest spreading email worm ever released: MyDoom. The MyDoom computer worm, sometimes called “Shimgapi” is spread via email and was intended to spread spam email messages via infected computers. It also launched a denial of service attack against SCO Group’s website, and created headaches for Google and other search engines. It is believed that the virus caused more than $38 billion in damages to computers and networks worldwide, making it one of the most costly computer virus to date.

#3: Melissa Virus

Melissa, which was released in March of 1999, was a mass-mailing macro virus that caused a lot of frustration by spreading itself to the first 50 people in an infected person’s address book. When it hit, it disrupted many email servers and caused more than $80 million in damages. But unlike pretty much every other virus on this list, we know who made this one! Because he used some code from another Macrovirus, David L. Smith was found to be responsible for the virus. He was arrested and sentenced to 10 years and a $5,000 fine. However, because he helped identify other internet troublemakers, he was released after 20 months.

#2: Sasser and Netsky

Let’s hope you have a firewall installed or you might as well let Sasser and Netsky come on in. Sasser is a worm connected to the Netsky family of viruses that attacks vulnerable PCs through an open port (That’s what your firewall protects against!). The release of the Sasser worm in 2004 caused widespread problems, including the cancellation of a number of Delta Air Lines trans-Atlantic flights. In addition, a hospital’s X-Ray machines went offline for hours, and a Nordic insurance company had to halt business in 130 offices. The culprit: a teenaged German boy named Sven Jaschan, who received a 21-month suspended sentence for being behind both the NetSky and Sasser worms.

Before we unveil our top pick, here are a few honorable mentions:
- PoisonIvy
- Oompa-Loompa [aka Leap.A]

#1: ILOVEYOU [aka Love Bug]

In 2000, a worm called ILOVEYOU was spread across the Internet via trusted email contacts. Those who opened the attachment included in the email (called Love Letter For You) became infected with a worm that quickly caused up to $8 billion in damage worldwide. ILOVEYOU was particularly effective due to most users’ general ignorance at the time. As it spread, it caused damage to local computers by randomly overwriting MS Office, image, and audio files before copying itself to all contacts in someone’s Microsoft Outlook address book. More than 50 million infections were reported within 10 days, with the virus costing approximately $15 billion to remove completely.


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