The Worst Computer Viruses in History


Computer viruses can be reasonably harmless, simply reducing your computer’s performance or displaying joke messages. Others have gotten way out of hand. Early on, even the most widespread viruses were reasonably harmless, simply the handiwork of bored geeks who wanted to see what they could do. As time went on, authors started using viruses to extort money from people, and governments used them to attack foreign countries’ computer infrastructure. Let’s take a look at some of the worst computer viruses in history.

Melissa: Don’t be fooled by the name

It all started with a Microsoft Word document upload on the 26th of March 1999 to a newsgroup on a website called Usenet. Its creator, David Smith, had been tracking the rise of a new kind of virus which could spread itself via e-mail. His own iteration, Melissa, was not the first, but it took e-mail viruses to previously unseen heights. It came in an e-mail with the subject line “important message from [name]” and contained a small Word document. When opened, it overrode Word’s security safeguards and sent itself to the first 50 contacts in the user’s Outlook address book. It spread like wildfire, and it wasn’t long until Microsoft was forced to shut down all incoming e-mail company-wide.

Stuxnet: Cyberwarfare comes to the fore

In the 90s, viruses like Melissa were annoying, but ultimately were not that malicious. Fast forward ten years and the circumstances had drastically changed. First uncovered in 2010, a virus called Stuxnet was propagating itself through computer systems which controlled industrial machinery, causing irreparable harm and disruption. It was a marksman’s virus; only a very specific set of industrial computers running certain software from the German company Siemens were affected. For this reason, it is widely believed that the virus was a joint U.S.-Israeli cyberattack to disrupt Iran’s nuclear program – which it did, as almost 60% of the infected computers were in that country.

WannaCry: A malicious get-rich-quick scheme

Meanwhile, malicious viruses were also evolving to affect personal computers. The U.S. National Security Agency developed an exploit for Microsoft Windows named EternalBlue, which allowed them to install malware on computers overseas. Unfortunately for them, it was stolen and used for a massive ransomware attack in 2017 called WannaCry. Ransomware is a name for viruses which encrypt your files, denying access to them until a payment is made to a specified account – in this case, a bitcoin wallet.

Europol estimated that 200,000 computers across 150 countries were affected, and around $150,000 worth of payments were made to the account. For their part, the U.S. Government, United Kingdom and Australia publicly stated they believed North Korea was behind the attack.

CryptoLocker: Hitting the jackpot

WannaCry was disruptive, causing major shutdowns to organisations like Britain’s National Health Service. However, the money the authors made was comparatively low. That was not the case for another major ransomware attack in 2014.

CryptoLocker, a trojan that targeted computers running on Microsoft Windows, spread itself via an e-mail which contained a .exe file attachment which had its icon changed to make it look like a more harmless .pdf document. Once opened, it encrypted the user’s files and demanded payment in the form of bitcoin or a prepaid cash voucher. It was an unprecedented success for the authors, managing to extort around $3 million.

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