Top 10 Most Dangerous and Destructive Computer Viruses In human History

A computer virus is a malicious software, programmed onto a user’s computer without his/her knowledge and could potentially performs malicious actions. It is capable of copying itself has a detrimental effect, such as corrupting the system and destroying data.

Here are the top 10 most destructive and dangerous viruses in human history:


In the year 2000’s the I LOVE YOU virus worked by sending a bogus “love letter” that looked like a harmless text file. It sends copies of itself to every e-mail address in the infected machine’s contact list. Shortly after its May 4 release, it had spread to more than 10 million PCs.

The virus was created by a college student in the Philippines named Onel de Guzman. He wrote the virus to steal passwords so he could log into different online services he wanted to use for free. He said that he had no idea how far his creation would spread.


Also known as Novarg. This virus caused an estimated damage of $38 billion in 2004 but its inflation-adjusted cost is actually $52.2 billion. Mydoom scraped addresses from infected machines, then sent copies of itself to those addresses. It also roped those infected machines into a web of computers called a botnet that performed distributed denial of service (DDoS) attacks. These attacks were intended to shut down a target website or server.

It has taken on a life of its own, infecting enough poorly-protected machines to send 1.2 billion copies of itself per year, 16 years after its creation.


The 2003 Sobig computer virus is actually another worm. It caused a damage estimated to $30 billion figure. In worldwide total, it includes Canada, U.K., the U.S., mainland Europe, and Asia. Several versions of the worm were released in quick succession, named Sobig A through Sobig F.

This program masqueraded as a legitimate computer software attached to emails. It disrupted ticketing at Air Canada and interfered with countless other businesses. Despite its widespread damage, the creator of the successful bug was never caught.


With nearly $20 billion in estimated damages, Klez infected about 7.2% of all computers in 2001. This worm sent fake emails, spoofed recognized senders and, among other things, attempted to deactivate other viruses.

As with other viruses and worms, it was released in several variants. It infected files, copied itself, and spread throughout each victim’s network. It hung around for years, with each version more destructive than the last.


The 2017 WannaCry computer virus is ransomware. It takes over your computer (or cloud files) and holds them hostage. The WannaCry ransomware ripped through computers in 150 countries, causing massive productivity losses as businesses, hospitals, and government organizations that didn’t pay were forced to rebuild systems from scratch.


The Zeus computer virus is an online theft tool that hit the web in 2007. A whitepaper by Unisys three years later estimated that it was behind 44% of all banking malware attacks. By then, it had breached 88% of all Fortune 500 companies, 2,500 organizations total, and 76,000 computers in 196 countries.

The Zeus botnet was a group of programs that worked together to take over machines for a remote “bot master.” It originated in Eastern Europe and was used to transfer money to secret bank accounts. More than 100 members of the crime ring behind the virus, mostly in the U.S., were arrested in 2010. It’s not as prominent today, but some of the virus’ source code lives on in newer botnet viruses and worms.


This malware attacked upwards of 250,000 machines by encrypting their files. It displayed a red ransom note informing users that “your important files encryption produced on this computer.” A payment window accompanied the note. The virus’ creators used a worm called the Gameover Zeus botnet to make and send copies of the CryptoLocker virus.

According to a report by security firm Sophos, the average ransomware attack costs a business $133,000. By estimation, CryptoLocker hit 5,000 companies, that would put its total cost at about $665 million.


First observed in 2001, the Code Red computer virus was yet another worm that penetrated about 975,000 hosts. It displayed the words “Hacked by Chinese!” across infected web pages, and it ran entirely in each machine’s memory. In most cases it left no trace in hard drives or other storage.

The financial costs are pegged at $2.4 billion. The virus attacked websites of infected computers and delivered a distributed denial of service (DDoS) attack on the U.S. White House’s website, In fact, the White House had to change its IP address to defend against Cod Red.


The SQL Slammer worm cost an estimated $750 million across 200,000 computer users in 2003. This computer virus randomly selected IP addresses, exploiting vulnerabilities and sending itself on to other machines. It used these victim machines to launch a DDoS attack on several internet hosts, significantly slowing internet traffic.

The Slammer worm hit banks in the U.S. and Canada especially hard, taking ATMs offline in many locations. Customers of Toronto’s Imperial Bank of Commerce found themselves unable to access funds. The attack reared its ugly head again in 2016, launching from IP addresses in Ukraine, China, and Mexico.


The Sasser worm was written by a 17-year-old German computer science student named Sven Jaschan. He was arrested at the age of 18 in 2004 after a $250,000 bounty was posted for the computer virus’ creator. A friend of Jaschan’s tipped authorities that the youth had penned not only the Sasser worm but also the damaging Netsky.AC attack.

Jaschan was given a suspended sentence after it was found he was a minor when he wrote the malware. The Sasser worm crashed millions of PCs, and though some reports put damages at $18 billion, the relatively low infection rate suggests a more likely cost of $500 million.


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