When we talk about a computer virus, we usually mean any kind of code that’s designed to do harm and spread itself to more computers.
They’re created by malicious programmers who might want to use your computer to attack other targets, or make money by stealing your personal information. They could also just be trying to see how far their virus will spread.
Different viruses can affect Windows, Mac and Linux computers, and even the data servers that keep companies, and the internet itself, running.
Antivirus programs help, but they can have trouble dealing with threats they’ve never seen before.Over the years, there have been thousands and thousands of viruses spread online, and they’ve caused billions of dollars of damage from lost productivity, wasted resources, and broken machines.
A few dozen of those viruses stand out, some spread especially quickly, or affected a lot of people, or created a ton of damage all by themselves. Some did all of the above.
Since a lot of viruses were very bad, in a lot of different ways, it’s hard to pick out which ones were objectively the worst.
Here are five most dangerous computer viruses of all time:
Perhaps the most virulent computer virus ever created, the ILOVEYOU virus managed to wreck PCs all across the world. Infecting almost 10% of the world’s PCs connected to the Internet, the virus caused a total damage of around $10 billion.
The virus apparently got transmitted via email with a subject line “ILOVEYOU,” which is a radical human emotion that no one can ignore. To make it even more alluring, the email contained an attachment that read something like this: Love-Letter-For-You.TXT.vbs. The moment someone opened the file, the virus emailed itself to the first 50 contacts available in the PC’s Windows address book.
Melissa became the breaking news on March 26, 1999, after hitting the new age of emailing. Built by David L, Melissa was spread in the form of an email attachment by the name “list.doc.”
When a person clicked upon the attachment, the virus would find the Microsoft Outlook address book and email itself to the first 50 contacts on the list having a message “Here is that document you asked for…donot show anyone else.” Later on, FBI arrested David L and slapped him with a fine of $5000 for creating the wildest virus of its time.
3. My Doom
My Doom hit the malware world in 2004 and spread exponentially through email with random addresses of senders and subject lines. Infecting somewhere around two million PCs, My Doom smashed the cyber world by instigating a tremendous denial of service attack. It transmitted itself via email in a specially deceitful way that a receiver would first consider a bounced error message that read “Mail Transaction Failed.”
However, as soon as the receiver clicked upon the message, the attachment executed and the worm transmitted to email addresses found in the user’s address book. It is easy to believe that this mass mailer worm caused a damage of almost $38 billion.
4. Code Red
Taking advantage of the Microsoft Internet Information Server’s flaw, Code Red spread on the network servers in 2001. Here is an amusing fact about this dangerous virus—it didn’t need you to open an email attachment or execute a file; it just required an active Internet connection with which it ruined the Web page that you opened by displaying a text “Hacked by Chinese!” It’s no surprise that this virus devastated nearly $2.6 billion dollars by hitting almost one million PCs.
And in less than a week’s time, the virus brought down over 400,000 servers that included the White House Web server as well.
Sasser was a Windows worm that was discovered in 2004. Apparently, it would slow down and crash the PC, making it even hard to reset without cutting the power. And its effects were surprisingly troublesome as well, with millions of PCs being infected and crucial, significant infrastructure affected.
The worm played on a buffer overflow susceptibility in Local Security Authority Subsystem Service (LSASS) that monitors the safety policy of local accounts causing crashes to the PC. The devastating effects of the virus were massive resulting in over a million infections. This included critical infrastructures, such as new agencies, hospitals, airlines, and public transportation.
Computers are amazing, but they just do what they’re told, and when viruses tell them to do bad things, it can create a lot of damage.
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