Zero-Day Exploit Examples (2024): The 10 Worst Attacks Ever

By Tibor Moes / Updated: January 2024

Zero-Day Exploit Examples (2023): The 10 Worst Attacks Ever

Zero-Day Exploits represent a significant cybersecurity threat, as they leverage unknown vulnerabilities in software before developers have a chance to address them. In this article, we will explore the ten most devastating Zero-Day Attacks in history, providing insightful statistics and analyses to understand their impact and lessons learned.


A Zero-Day Exploit is a cyber attack that occurs on the same day a weakness is discovered in software, before the creator has a chance to fix it.

  • Code Red Worm (2001): This worm exploited a vulnerability in Microsoft IIS servers and spread rapidly worldwide. It infected over 359,000 systems in less than 14 hours, causing an estimated $2 billion in damages.
  • SQL Slammer (2003): A fast-spreading worm that caused widespread internet outages by targeting Microsoft SQL Server and MSDE. It affected approximately 250,000 computers globally.
  • Sasser Worm (2004): Sasser spread by exploiting a vulnerability in Windows systems, causing considerable disruption. It infected about two million computers worldwide.
  • Stuxnet Worm (2010): A sophisticated cyber weapon aimed at Iran’s nuclear program, causing physical damage to centrifuges. It infected over 200,000 computers and caused 1,000 machines to physically degrade.
  • Heartbleed (2014): A critical flaw in OpenSSL that allowed sensitive data to be stolen from servers. Heartbleed potentially affected over 500,000 websites at the time of its discovery.
  • Shellshock (2014): This bug in the Bash shell enabled hackers to execute commands on Unix systems. CloudFlare reported blocking around 1.1 million Shellshock attacks.
  • Petya/NotPetya (2017): Masquerading as ransomware, this attack caused widespread damage and data loss. It resulted in over $10 billion worth of global damage.
  • WannaCry (2017): A ransomware attack that spread across 150 countries, infecting around 200,000 computers. The financial losses from the attack could reach up to $4 billion.
  • Spectre and Meltdown (2018): Hardware vulnerabilities in processors that put data at risk on millions of devices. Around 1.7 billion smartphones were vulnerable to these exploits.
  • BlueKeep (2019): A vulnerability in Microsoft’s Remote Desktop Protocol that put millions of Windows systems at risk. Initial estimates suggested 7.6 million systems could be attacked, later adjusted to 950,000.

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Zero-Day Exploit Examples

1. Code Red Worm (2001)

In the summer of 2001, the digital world witnessed one of the most aggressive cyber attacks of its time – the Code Red worm. This malicious software spread with unprecedented speed, infecting over 359,000 systems globally in less than 14 hours, a statistic highlighted in a detailed study by ResearchGate.

The worm exploited a vulnerability in Microsoft’s Internet Information Server (IIS), which was widely used for hosting websites. Once infected, the systems became part of a network that launched attacks on other vulnerable servers, exponentially increasing the worm’s spread.

The financial implications were staggering. The total damage caused by the Code Red worm was estimated to exceed $2 billion. This cost was not just in terms of the immediate impact on infected systems but also in the subsequent global effort to bolster cybersecurity defenses.

The Code Red worm served as a wake-up call, demonstrating the need for more robust security measures in an increasingly interconnected world.

2. SQL Slammer (2003)

Just two years later, in January 2003, another major cyber threat emerged: the SQL Slammer worm. This worm targeted a vulnerability in Microsoft SQL Server and MSDE, rapidly infecting systems across the globe.

According to a report by WeLiveSecurity, over 250,000 computers were thought to have been affected worldwide. SQL Slammer’s impact was profound, not just in terms of the number of infected computers, but also in its ability to disrupt essential services. It caused widespread internet outages, affecting banks, airlines, and even emergency services, highlighting the vulnerability of critical infrastructure to cyber threats.

SQL Slammer’s proliferation was a clear indication of how quickly a well-crafted exploit could spread through the digital ecosystem. It underscored the importance of timely software updates and the need for constant vigilance in the fight against cyber threats.

The aftermath of SQL Slammer contributed significantly to the evolution of cybersecurity practices and the adoption of more rigorous protocols to protect against such vulnerabilities.

3. Sasser Worm (2004)

In 2004, the digital world grappled with a new kind of menace: the Sasser worm. Unlike its predecessors, Sasser didn’t require users to open an email attachment to spread; instead, it exploited a vulnerability in Windows operating systems to propagate itself across networks.

This worm and its variants infected approximately two million computers globally, as noted on Wikipedia. The impact of Sasser was widespread, affecting personal users, businesses, and even critical infrastructure. Organizations worldwide faced significant disruptions, with computers continually rebooting or becoming inoperable.

The Sasser worm was a pivotal moment in cybersecurity, demonstrating the devastating effects of network worms. It highlighted the necessity for regular software updates and the importance of robust security protocols in networked environments.

The widespread damage caused by Sasser spurred enhancements in antivirus technology and a more proactive approach to cyber threat detection and mitigation.

4. Stuxnet Worm (2010)

Stuxnet, discovered in 2010, marked a turning point in the history of cyber warfare. This sophisticated worm was designed to sabotage Iran’s nuclear program, and it did so with alarming precision. According to a report available via the Internet Archive, Stuxnet reportedly ruined almost one-fifth of Iran’s nuclear centrifuges.

It achieved this by targeting industrial control systems, specifically Siemens’ SCADA systems, which are commonly used in industrial sectors. The worm infected over 200,000 computers and caused physical degradation in approximately 1,000 machines.

Stuxnet’s design was ingenious, as it remained dormant until it reached its specific target, evading detection for a long time. The revelation of Stuxnet’s capabilities was a wake-up call to nations and industries about the potential for cyber attacks to cause physical damage to critical infrastructure.

It underscored the importance of securing not just IT systems but also operational technology (OT) systems, which are integral to the functioning of industrial and utility services. Stuxnet was a clear indicator of the evolving landscape of cyber threats, where digital attacks can have real-world consequences.

5. Heartbleed (2014)

In 2014, the cyber world was shaken by the discovery of Heartbleed, a security bug with the potential to bleed sensitive data from two-thirds of the internet’s websites. As reported by Pew Research Center, at the time of its discovery, Heartbleed potentially affected about 500,000 or more websites.

This vulnerability lay in the OpenSSL cryptographic software library, which meant that attackers could intercept secure communications that should have been protected by SSL/TLS encryption. From usernames and passwords to private keys and confidential communications, the risk was enormous.

The response to Heartbleed was urgent and widespread, involving a race to patch systems, revoke compromised keys, and reassure a worried public that their online transactions were secure.

Heartbleed was not just a bug; it was a stark reminder of the intrinsic vulnerabilities in the systems that underpin our digital lives. It brought to light the importance of open-source security and the need for ongoing investment in cybersecurity infrastructure.

6. Shellshock (2014)

In the same year, another vulnerability surfaced, known as Shellshock, which targeted the Bash shell, a common command processor used in many Unix systems. The scale of Shellshock’s threat was substantial, and the response needed to be swift.

The Verge reported that CloudFlare, a web-optimization company, blocked roughly 1.1 million Shellshock attack attempts. This flaw allowed attackers to execute arbitrary commands on affected systems, posing a threat to web servers, computers, routers, and even some Internet-of-Things devices.

The Shellshock vulnerability showcased the far-reaching implications of security weaknesses in widely used components of internet infrastructure. The defense against Shellshock was multifaceted, from patches and updates to heightened monitoring for unusual system behavior.

This incident was a critical lesson for the tech community in the need for comprehensive security reviews and the potential domino effect that a single vulnerability can trigger across the global network.

7. Petya/NotPetya (2017)

In 2017, a catastrophic cyberattack named Petya, later referred to as NotPetya, swept across the globe, causing chaos and confusion. Originating in Ukraine, the attack spread rapidly, affecting companies, government agencies, and institutions worldwide.

As Wired reports, the total damages from NotPetya were colossal, amounting to more than $10 billion globally. This malicious campaign masqueraded as ransomware but was, in fact, designed to cause disruption and destruction. Unlike typical ransomware, NotPetya did not offer a real means for victims to recover their data, leading to permanent loss of data and crippling critical systems.

The scale and sophistication of the NotPetya cyberattack underscored the destructive potential of digital weapons and the vulnerability of digital infrastructures worldwide. The incident became a case study in the importance of cyber hygiene, the risks of using outdated systems, and the critical need for international cooperation in cybersecurity.

8. WannaCry (2017)

WannaCry was a global cyber epidemic that struck in May 2017, targeting hundreds of thousands of computers with its ransomware attack.

According to Europol, via BBC News, around 200,000 computers were infected across 150 countries, making it an unprecedented ransomware campaign in terms of scale. The attack leveraged a vulnerability in older Windows operating systems to encrypt data and demand ransom for its release.

The estimated financial and economic losses from the WannaCry attack were monumental, potentially reaching up to $4 billion as reported by CBS News, which positioned it among the most damaging cyberattacks in history.

WannaCry was more than just a malware attack; it was a warning of the extensive damage that cyber threats can inflict on a global scale. It highlighted the critical necessity for regular updates and patches, the importance of backups, and the need for robust cybersecurity measures to protect against such pervasive threats.

The wake of WannaCry saw a concerted effort to strengthen cyber defenses and raise awareness about the importance of cybersecurity in our increasingly connected world.

9. Spectre and Meltdown (2018)

The year 2018 opened with the tech world grappling with the discovery of two significant vulnerabilities: Spectre and Meltdown. These issues struck at the heart of computer security, affecting the fundamental hardware—processors in computers and smartphones.

According to Statista, approximately 1.7 billion smartphones were vulnerable to these exploits, along with countless other devices. These vulnerabilities could allow attackers to access sensitive data stored in the memory of running programs, posing a risk to personal data, intellectual property, and even national security.

The revelation of Spectre and Meltdown brought to light the complexity and depth of hardware vulnerabilities, presenting a challenge that went beyond the realm of regular software patches. It prompted a significant reevaluation of processor design and a collaborative effort between hardware manufacturers, software developers, and cybersecurity professionals to mitigate the risks and protect user data across the globe.

10. BlueKeep (2019)

BlueKeep emerged as a critical security vulnerability in Microsoft’s Remote Desktop Protocol, affecting older versions of Windows operating systems. When it was first identified in 2019, ZDNet reported that initial estimates indicated nearly 7.6 million Windows systems connected to the Internet could be at risk of attack via the BlueKeep vulnerability. Later, a more refined assessment suggested the number was closer to 950,000—a still alarmingly high figure.

This vulnerability was particularly concerning because it had the potential to be wormable, meaning it could spread across systems without user interaction, similar to the devastating WannaCry attack.

The response to BlueKeep was a large-scale, coordinated effort to patch vulnerable systems and raise awareness among users and organizations about the importance of updating and securing their systems.

BlueKeep served as yet another crucial reminder of the ongoing risks posed by legacy systems and the essential need for proactive cybersecurity practices to prevent the exploitation of such vulnerabilities.


The revelations of the ten worst Zero-Day Exploits in history underscore the continuous and evolving threats that cyber attacks pose to global security and economy. From the early days of the Code Red Worm to the more recent BlueKeep vulnerability, each incident has highlighted the vulnerability of digital infrastructures and the importance of cybersecurity vigilance.

As we navigate an increasingly digital world, the necessity of robust cybersecurity measures cannot be overstated. For users of the latest operating system, Windows 11, investing in reputable antivirus software is crucial. Brands like Norton, Avast, TotalAV, Bitdefender, McAfee, Panda, and Avira offer sophisticated solutions designed to detect, prevent, and respond to a myriad of cyber threats.

These tools not only provide real-time protection against known threats but also use advanced heuristics and machine learning to anticipate and defend against new, emerging threats. In conclusion, the investment in a solid antivirus software is not just a safeguard for our personal data but a critical component in the defense of our collective digital ecosystem.




Author: Tibor Moes

Author: Tibor Moes

Founder & Chief Editor at SoftwareLab

Tibor has tested 39 antivirus programs and 30 VPN services, and holds a Cybersecurity Graduate Certificate from Stanford University.

He uses Norton to protect his devices, CyberGhost for his privacy, and Dashlane for his passwords.

You can find him on LinkedIn or contact him here.