Malware, short for malicious software, refers to any software intentionally designed to cause harm to computers, servers, or networks. A malware attack is a cybercrime in which an attacker installs malicious software on a victim’s system, typically to steal sensitive information or gain financial benefit.
Cybercriminals commonly spread malware through deceptive methods such as dangerous pop-ups, suspicious links, malicious email attachments, and compromised downloads.
Below, we look at some of the most devastating malware attacks of all time.
In 2000, Michael Calce, also known as MafiaBoy, a teenager from Canada, caused widespread disruption across the internet by launching a series of Distributed Denial-of-Service (DDoS) attacks. These attacks targeted major websites including Yahoo!, Amazon, CNN, and eBay.
Calce claimed he unknowingly entered multiple IP addresses into a security tool he had downloaded online. Regardless of intent, the attacks brought down Yahoo—then the most widely used search engine—and shut down several other high-profile websites for hours.
As a juvenile offender, he received an eight-month sentence, was placed under strict supervision, and had his internet access heavily restricted.
In 1999, Jonathan James, a 15-year-old hacker from the United States, became the first juvenile convicted of hacking crimes. He gained unauthorized access to NASA and the U.S. Department of Defense, stealing confidential information including usernames, passwords, and sensitive military software used for space exploration.
The breach forced NASA to shut down its entire network for three weeks, costing the agency millions of dollars.
James received a reduced sentence due to his age. Tragically, he died by suicide in 2008 after being accused—claims he denied—of involvement in another hacking case, as stated in his suicide note.
The Sony Pictures hack shocked the world and dominated headlines. U.S. authorities linked the attack to the release of “The Interview”, a comedy film depicting the assassination of North Korea’s leader, Kim Jong-un.
A group calling itself “Guardians of Peace” claimed responsibility and demanded the film’s cancellation. The attackers leaked massive amounts of confidential data, including executive salaries, private emails, celebrities’ phone numbers, and unreleased Sony films—making it one of the most damaging corporate cyberattacks ever.
The WannaCry ransomware attack is one of the most notorious cyberattacks in history. It exploited a Windows vulnerability known as EternalBlue, affecting hundreds of thousands of computers across more than 100 countries.
WannaCry encrypted victims’ files and demanded a ransom of $300 in Bitcoin to restore access. The attack severely impacted businesses, governments, and hospitals—forcing many healthcare providers to cancel critical appointments.
Microsoft later released patches to address the EternalBlue vulnerability.
Stuxnet is widely regarded as the most dangerous malware ever created. Discovered in 2010, this sophisticated worm spread via USB drives and infected Windows systems.
Its target was highly specific: the centrifuges used in Iran’s nuclear enrichment facilities. Stuxnet caused physical damage by subtly altering centrifuge speeds, reportedly forcing Iran to shut down operations at facilities such as Bushehr for weeks.
Often described as the world’s first cyberweapon, Stuxnet has been widely attributed—though never officially confirmed—to state-sponsored actors, with the U.S. and Israel frequently mentioned.
NotPetya, also known as ExPetr, was initially disguised as ransomware but was, in reality, a data-destroying malware. Like WannaCry, it exploited EternalBlue and EternalRomance vulnerabilities to spread rapidly.
Unlike ransomware, NotPetya had no real recovery mechanism—its sole purpose was destruction. It primarily targeted businesses across Europe, the U.S., and Asia.
With estimated damages of $10 billion, NotPetya is considered the costliest malware attack of all time, surpassing WannaCry’s $5–$8 billion impact.
The Melissa virus, released in March 1999, was named after a stripper by its creator, David L. Smith. It targeted Microsoft Word and spread via Microsoft Outlook by emailing itself to the first 50 contacts in a victim’s address book.
The virus used enticing attachment names like “sexxxy.jpg” or “Here is the document you requested… don’t show anyone else ;-)”, causing it to spread rapidly.
Although Melissa wasn’t designed for financial theft, it caused massive disruption—forcing organizations, including Microsoft, to shut down email servers. Smith was arrested in New Jersey in April 1999 and later sentenced to 20 months in prison and fined $5,000.
The ILOVEYOU virus, also known as the Love Letter Worm, exploited human curiosity and emotion. Created by Onel de Guzman, a student from the Philippines, it spread via email with the subject line “ILOVEYOU” and a malicious attachment.
Once opened, the virus forwarded itself to all contacts and deleted or overwrote files such as MP3s, JPEGs, CSS, and system scripts. It also modified Windows registry settings and spread through Internet Relay Chat (IRC).
In 2000, the virus infected over 500,000 computers worldwide, causing an estimated $15 billion in damages.
To reduce your risk of malware attacks: