The World's Most Dangerous Computer Viruses

Here are five most dangerous computer viruses of all time:

1. ILOVEYOU

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 is 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.

2. Melissa

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.

5. Sasser

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.

6. Conficker

Also known as Downup or Downadup, Conficker is a worm of unknown authorship for Windows that made its first appearance in 2008. The name comes form the English word, configure and a German pejorative.It infects computers using flaws in the OS to create a botnet. The malware was able to infect more than 9 millions computers all around the world, affecting governments, businesses and individuals. It was one of the largest known worm infections to ever surface causing an estimate damage of $9 billion.

The worm works by exploiting a network service vulnerability that was present and unpatched in Windows. Once infected, the worm will then reset account lockout policies, block access to Windows update and antivirus sites, turn off certain services and lock out user accounts among many. Then, it proceeds to install software that will turn the computer into a botnet slave and scareware to scam money off the user. Microsoft later provided a fix and patch with many antivirus vendors providing updates to their definitions.

7. Flashback

Though not as damaging as the rest of the malware on this list, this is one of the few Mac malware to have gain notoriety as it showed that Macs are not immune. The Trojan was first discovered in 2011 by antivirus company Intego as a fake Flash install. In its newer incarnation, a user simply needs to have Java enabled (which is likely the majority of us). It propagates itself by using compromised websites containing JavaScript code that will download the payload. Once installed, the Mac becomes part of a botnet of other infected Macs.

The good news is that if it is infected, it is simply localized to that specific user’s account. The bad news is that more than 600,000 Macs were infected, including 274 Macs in the Cupertino area, the headquarters of Apple. Oracle published a fix for the exploit with Apple releasing an update to remove Flashback from people’s Mac. It is still out in the wild, with an estimate of 22,000 Macs still infected as of 2014.a

 

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.