1. CryptoLocker

When it comes to malware, ransomware is the new kid on the block. While most people can rattle off names like ‘Trojan’, ‘viruses’, and ‘spyware’, they’re often not too familiar with ransomware.

Ransomware is a kind of malware that takes your files hostage. You know in heist movies when the bad guy grabs someone and threatens them in return for money? Ransomware works much like that, except your computer is taken hostage by a faceless bad guy.

Released in September 2013, CryptoLocker spread through email attachments and encrypted the user’s files so that they couldn’t access them.

The hackers then sent a decryption key in return for a sum of money, usually somewhere from a few hundred pounds up to a couple of grand.

With some of the hacking attempts, System Restore or recovery software worked. Although with many of the infected computers, if the victims didn’t pay up they’d lose all their files. Now is a good time to remind you to always back your files up!

In June 2014, Operation Tovar took down Evgeniy Bogachev, the leader of the gang of hackers behind CryptoLocker. In February, the FBI offered a cool $3 million reward for Bogachev.

Cost of the malware: With 500,000 victims, CryptoLocker made upwards of $30 million in 100 days. 

2. ILOVEYOU

While ILOVEYOU sounds like a cheerful bon mot you might find printed on the inside of a Valentine’s Day card, it’s actually far, far more sinister than that. ILOVEYOU is one of the most well-known and destructive viruses of all time.

It’s been 15 years since ILOVEYOU was let loose on the internet. By today’s standards it’s a pretty tame virus, but in 2000 it was the most damaging malware event of all time. Likely, ILOVEYOU inspired many hackers to wield their keyboard as a weapon.

But why was it so brutal? 

Source: Shutterstock

Well, in 2000 malware was a bit of a myth. In fact, it was such a myth that malware could get away with being completely unsubtle. If you got an email today like the one that was sent around in 2000, you’d never open it. (We hope!) The virus came in an email with a subject line that said “I love you”.

Being curious types, people clicked into the email with aplomb—regardless of the fact the email wasn’t from anyone they knew.

The malware was a worm that was downloaded by clicking on an attachment called ‘LOVE-LETTER-FOR-YOU.TXT.vbs’.

ILOVEYOU overwrote system files and personal files and spread itself over and over and over again. ILOVEYOU hit headlines around the world and still people clicked on the text—maybe to test if it really was as bad as it was supposed to be. Poking the bear with a stick, to use a metaphor.

ILOVEYOU was so effective it actually held the Guinness World Record as the most ‘virulent’ virus of all time. A viral virus, by all accounts. Two young Filipino programmers, Reonel Ramones and Onel de Guzman, were named as the perps but because there were no laws against writing malware, their case was dropped and they went free.

Cost of the malware: $15 billion.

3. MyDoom

MyDoom is considered to be the most damaging virus ever released—and with a name like MyDoom would you expect anything less?

MyDoom, like ILOVEYOU, is a record-holder and was the fastest-spreading email-based worm ever. MyDoom was an odd one, as it hit tech companies like SCO, Microsoft, and Google with a Distributed Denial of Service attack.

25% of infected hosts of the .A version of the virus allegedly hit the SCO website with a boatload of traffic in an attempt to crash its servers.

As well as targeting tech companies, MyDoom spammed junk mail through infected computers, with the text that said “andy; I’m just doing my job, nothing personal, sorry”. Who was Andy? Who knows.

In 2004, roughly somewhere between 16-25% of all emails had been infected by MyDoom.

Cost of the malware: $38 billion. 

4. Storm Worm

Storm Worm was a particularly vicious virus that made the rounds in 2006 with a subject line of ‘230 dead as storm batters Europe’. Intrigued, people would open the email and click on a link to the news story and that’s when the problems started.

Storm Worm was a Trojan horse that infected computers, sometimes turning them into zombies or bots to continue the spread of the virus and to send a huge amount of spam mail.

Tip: never open a link in an email unless you know exactly what it is.

By July 2007, Storm Worm was picked up in more than 200 million emails.

Cost of the malware: An exact cost is yet to be calculated. 

5. Sasser & Netsky

17-year-old Sven Jaschan created Sasser & Netsky, two worms, in the early noughties. Sasser & Netsky are actually two separate worms, but they’re often grouped together because the similarities in the code led experts to believe they were created by the same person.

Sasser spread through infected computers by scanning random IP addresses and instructing them to download the virus. Netsky was the more familiar email-based worm. Netsky was actually the more viral virus, and caused a huge amount of problems in 2004.

A German student, Jaschan was arrested when multiple tip-offs were reported to the police. Speculation suggested Jaschan had actually written the viruses to create business for his mother and stepfather’s PC business. Because he was under 18 when he wrote the virus, Jaschan spent his prison sentence on probation.

Even more interesting is Jaschan’s motivation. MyDoom was spreading rapidly at the time and Jaschan, a newbie coder, wanted to see what would happen if his bug could spread faster than MyDoom. Things quickly escalated from there.

Sasser was so effective it actually ground one third of the post offices in Taiwan to a halt, shut down 130 branches of a Finnish bank, and forced rail and transatlantic flights to be cancelled.

Cost of malware: Around $31 billion.

6. Anna Kournikova

What’s a tennis player got to do with a list of interesting viruses? Quite a lot, as it so happens.

We’re going to get this out of the way first: the Anna Kournikova virus is pretty tame compared to many on the list.

So in the early to mid-noughties, Anna Kournikova was one of the most searched terms on the internet. People were just very into tennis.

Jan De Wit, a 20-year-old Dutch man, wrote the virus as ‘a joke’. The subject was “Here you have, ;0)” with an attached file called AnnaKournikova.jpg.vbs. Anna was pretty harmless and didn’t do much actual damage, though De Wit turned himself into police anyway.

The mayor of the town came forward and said the city should be proud to have produced such a talented young man and offered him a job as a techie once he was finished his education.

Cost of the malware: $166,000.

7. Slammer

While most of the malware on this list strictly hit computers, Slammer was created with broader ambitions. Slammer is the kind of virus that makes it into films, as only a few minutes after infecting its first victim, it was doubling itself every few seconds. 15 minutes in and Slammer had infected half of the servers that essentially ran the internet.

The Bank of America’s ATM service crashed, 911 services went down, and flights had to be cancelled because of online errors. Slammer, quite aptly, caused a huge panic as it had effectively managed to crash the internet in 15 quick minutes.

Cost of the malware: Around $1 billion.

Source: Stocksnap

8. Stuxnet

Stuxnet is easily the scariest virus on the list as it was built by government engineers in the US with the intention of obstructing nukes from being built in Iran.

Yes, you read that right. Who needs to target email when they can gun for nukes?

Stuxnet spread by a USB thumb drive and targeted software controlling a facility in Iran that held uranium. The virus was so effective it caused their centrifuges to self-destruct, setting Iran’s nuclear development back and costing a lot of money. 

Stuxnet is the first real venture into cyberwar and it definitely asks the question as to what will come next. The idea of digital weaponry is pretty scary, isn’t it?

Cost of the malware: Unknown.

So there you have it: while viruses and malware might seem like a myth drummed up by tech companies, they are a very real threat that have caused billions in damage.