Many of us at some point have found that our computer had started acting weirdly. Computer viruses basically act like viruses and replicate. They infect lots of files on a computer and also spread to another computer.
There are viruses like Worms, Adware, Trojans, and Rootkits which are hard to detect and can give attackers control of the machine. Perhaps even more frightening viruses are ransomware attacks, where someone gets a hold of the data and sometimes sensitive data that makes you pay to get it back.
Some of the known computer viruses are:
1. SQL Slammer / Sapphire
This caused havoc in the USA in 2003 and cost about $1B. It affected the web servers which eventually lead to bank ATMs crashing. It messed with continental airlines, electronic ticketing and it blocked 27 million people from the internet with even Seattle's 911 services affected.
Wired explained Slammer used a software attack with the infected computers spreading the worm through the internet. It infected around 75,000 servers in just 10 minutes. It was then stopped by patches and antivirus software. The creator of this virus remains unknown.
2. Melissa
This virus was named after an exotic dancer. It began as an infected Word document posted on an alt.sex Usenet group and if that was opened it would send itself to 50 people on some other person's Microsoft Outlook email program.
That might not sound too bad. But it created mayhem when emails were being sent at a rate that messed with companies and big corporations so much so that in 1999 Microsoft shut down incoming emails.
According to a source email users would get a message as 'Here is that document you asked for and don't show it to anyone else'. There was also an attachment with it. And it cost the governments, people, and companies all about $1.2B.
3. Anna Kournikova
This virus was created by a young 20-year-old Dutch guy named Jan De Wit. He used an apparent photo of the good-looking tennis player, Anna Kournikova as bait where if you clicked that file then it created a viral visual basic script that means everyone in the address book will be forwarded the same thing.
This affected millions of people which eventually overloaded the servers all over the world. According to a source the time after De Wit understood what the worm did he decided to turn himself into the police. He was lucky and got away with only 150 hours of community service. The virus was even in an episode of a sitcom named Friends.
4. Code Red
These estimates on the damage caused by Code Red range in the billions of Webpages that were affected and suddenly got the message 'Welcome to worm comm hacked by Chinese Norian'.
The malicious code was not saved as a file but is inserted into and then run directly from memory. It has been called one of the most sophisticated attacks ever that almost brought down the internet. Many websites ran on Microsoft Internet Information Server and was subject to this distributed denial-of-service attack which means the websites got overwhelmed with too much traffic that effectively brought them down.
According to Scientific American, it might not have been China who was the culprit though. Many investigations were conducted, but the culprit remains unknown.
5. Conficker
Conficker is said to be the most destructive worm of all time and cost those infected around $9B. This was discovered in 2008 and infected around fifteen million computers. It affected police departments in the UK as well as the military and messed with their operations. It infected Windows operating systems for a long time as it kept getting past antivirus software and patches. It was a mystery for security experts too, but they knew a machine infects other machines in the network.
6. ILOVEYOU
This virus came as an email with the words 'I love you' in the subject line. It's spread fast because people open that attachment file and once they did that everyone else in that address book got the same email and apart from that it also deleted many JPEG and MP3 files.
It reached around 45 million people in just a day. It became so huge that in 2000, Ford Motor Company shut down its email. It was almost the same as Melissa, but over here it sent a mail to all of your contacts and then deleted personal files too. Pentagon CIA and the British Parliament also shut down their emails. The virus was eventually linked to some young programmers in the Philippines and the cost of this virus was around $15B.