7 Biggest Cyber Attacks in History That Changed Security

Imagine turning on your computer only to find all your files encrypted, with a message demanding payment to regain access. This is exactly what happened to thousands of victims of WannaCry, one of the biggest cyberattacks in history.

Cyberattacks have targeted everything from personal data to critical infrastructure, leaving organizations struggling to recover. So, what can we learn from these events? Studying famous cyberattacks can teach important lessons about how to build stronger defenses and stay one step ahead of attackers. That's exactly what we'll explore in this article!

What Are Cyber Attacks?

Cyberattacks are deliberate attempts to disrupt, damage, or gain unauthorized access to computer systems, networks, or data. These attacks often target organizations, governments, and individuals, with goals like financial gain, disruption of operations, or access to sensitive information.

Cyber attackers use a variety of methods, including ransomware to encrypt data and demand payment, phishing to steal credentials, and distributed denial-of-service (DDoS) attacks to overwhelm systems and render them unusable. Unlike covert activities like cyber espionage, cyberattacks are usually quick, highly visible, and disruptive.

Here are some key characteristics of cyberattacks:

• Objectives. Financial extortion, disruption of services, or theft of personal and corporate data.
• Methods. Ransomware, phishing, DDoS attacks, malware, and exploiting software vulnerabilities.
• Targets. Businesses, government agencies, healthcare institutions, financial organizations, and individual users.

Examples of cyberattacks include high-profile ransomware incidents like WannaCry, which affected hundreds of thousands of systems globally, and large-scale data breaches that exposed millions of user accounts.

7 Biggest Cyber Attacks in History

Looking back at the biggest cyberattacks in history helps identify recurring patterns. Many of these famous cyberattacks introduced new tactics or exploited unpatched vulnerabilities. Reviewing these incidents offers lessons on preparedness and prompt response.

Some consistent themes include:

• Poor patch management allowed malware to spread.
• Lack of encryption exposed personal and financial data.
• Slow incident response magnified damage.
• Limited employee awareness enabled phishing success.

Below are the seven biggest cyberattacks that highlight different aspects of global cyber threats.

WannaCry

WannaCry ranks high among the biggest cyber attacks in history. It emerged in May 2017, spreading rapidly across approximately 150 countries and infecting over 200,000 devices. The attackers leveraged a known Windows vulnerability (EternalBlue), previously patched by Microsoft, but many organizations failed to apply the patch.

Key features of WannaCry:

• Method. Ransomware encrypted files and demanded Bitcoin payments.
• Impact. Healthcare systems, transport networks, and corporate servers were disrupted.
• Notable victim. UK’s National Health Service (NHS), causing appointment cancellations and delays.
• Recovery step. A kill switch domain halted further spread.
• Lesson learned. Prompt patching, offline backups, and strict endpoint protection reduce ransomware risk.

WannaCry proved that even a known vulnerability could trigger a major cyberattack if organizations delay updates. This case reinforces that strong patching and fast detection are the best defenses against such attacks.

The Yahoo Data Breach

The Yahoo data breach is one of the biggest cyberattacks in history due to its unprecedented scale and far-reaching consequences. In 2013 and 2014, attackers compromised billions of accounts, making it one of the most extensive breaches ever recorded. The breach wasn't disclosed until years later, leading to outrage, legal challenges, and a major loss of user trust.

Attackers gained access to Yahoo's systems through weak encryption and spear phishing. Once inside, they retrieved sensitive user information, including names, email addresses, phone numbers, dates of birth, hashed passwords, and security questions. This breach exposed users to identity theft and financial fraud, with many facing spam campaigns and phishing attempts using the stolen data.

Key features of the Yahoo breach:

• Data exposed. Names, email addresses, dates of birth, hashed passwords, phone numbers, security questions.
• Method. Spear phishing and weak encryption methods exploited by attackers.
• Impact. Identity theft risks, spam campaigns, erosion of user trust.
• Company response. Users were advised to reset passwords, adopt MFA, and monitor accounts.
• Lesson learned. Strong encryption, timely breach disclosure, and proper incident response planning matter.

Yahoo's delayed disclosure made the situation worse, making people doubt their ability to protect user data. Lawsuits, regulatory penalties, and a $350 million reduction in Yahoo’s acquisition price by Verizon followed. This breach highlights the importance of proactive security measures, strong encryption, and transparency during incidents. It also serves as a reminder that even huge tech companies are vulnerable to cyberattacks.

PlayStation Network Hack

The 2011 PlayStation Network (PSN) hack shocked the gaming industry, becoming one of the biggest cyberattacks on an entertainment platform. Attackers gained access to sensitive data from approximately 77 million user accounts, forcing Sony to shut down the PSN for 23 days. This disruption left gamers unable to access their accounts or play online, causing widespread frustration.

The breach exposed critical information, including usernames, addresses, passwords, and financial details such as credit card numbers. Sony faced significant backlash for its handling of the incident, with users demanding better protection for personal data. The financial cost of the attack was estimated at $171 million, which included expenses for rebuilding the network, compensating users, and improving security measures.

Key features of the PSN hack:

• Data exposed. Usernames, addresses, passwords, and financial details.
• Impact. Estimated $171 million in losses, significant downtime, and user frustration.
• Response. Sony rebuilt the network with better security, offered identity theft insurance, and provided complimentary services.
• Lesson learned. Weak network infrastructure invites cyberattacks. Strengthening security layers and transparency after incidents improves user trust.

The PSN hack highlighted the vulnerability of consumer platforms and the importance of robust defenses in the entertainment industry. Sony’s response included rebuilding the network with stronger infrastructure, offering identity theft insurance, and providing free content to affected users.

NotPetya

NotPetya, which emerged in June 2017, is one of the biggest cyberattacks due to its impact on global supply chains and businesses. Unlike typical ransomware, NotPetya didn't provide victims a way to recover their encrypted data, making it more destructive than financially motivated. It caused billions of dollars in damage and disrupted critical industries worldwide.

The malware initially spread through a Ukrainian accounting software update, exploiting vulnerabilities such as EternalBlue and Mimikatz to move laterally across networks. Within hours, it infected systems in multiple countries, affecting ports, freight terminals, food producers, and pharmaceutical companies. Maersk, a global shipping giant, was among the most notable victims, forced to rebuild thousands of servers and tens of thousands of PCs to restore operations.

Key features of NotPetya:

• Method. Initially spread through Ukrainian accounting software updates, then used EternalBlue and Mimikatz exploits.
• Impact. Crippled ports, freight terminals, food producers, and pharmaceutical firms.
• Notable victim. Maersk, forced to rebuild thousands of servers and PCs.
• Lesson learned. Network segmentation, consistent patching, and well-tested incident response plans help limit damage.

NotPetya demonstrated how rapidly cyber attacks can cripple global operations. It underscored the importance of resilience, emphasizing good patch management, strong incident response plans, and network segmentation.

Operation Aurora

Operation Aurora, revealed in 2010, was an advanced Chinese cyber espionage campaign targeting major tech companies, including Google. This attack showed how complex state-sponsored operations can be and how even the most secure organizations are vulnerable. The attackers used zero-day vulnerabilities in Internet Explorer to infiltrate systems and access sensitive corporate data.

The primary goal was to steal intellectual property and confidential communications. Google was hit particularly hard, leading the company to rethink its international operations. Other tech and defense corporations were also at risk as attackers sought strategic information that could provide competitive or geopolitical advantages.

Key features of Operation Aurora:

• Method. The attackers exploited zero-day vulnerabilities in Internet Explorer to steal intellectual property and sensitive communications.
• Impact. Stolen corporate secrets, strategic information at risk, and a shift in Google’s operations abroad.
• Lesson learned. Countering cyber espionage requires vigilance, advanced security controls, and continuous code review.

Operation Aurora stands as one of the biggest cyber attacks targeting intellectual property. It introduced the world to a more stealthy form of intrusion and remains a prime example of cyber espionage.

Target Data Breach

The Target data breach, one of the most infamous retail cyberattacks, affected over 40 million customers during the holiday season in 2013. Hackers accessed Target’s payment system by exploiting weak credentials from a third-party vendor. They installed malware on point-of-sale (POS) terminals, stealing customers' payment card information.

Key features of the Target breach:

• Data exposed. Payment card details, including credit and debit card numbers, names, and security codes.
• Method. Malware installed on POS terminals via a third-party vendor's compromised access.
• Impact. Loss of customer trust, financial damages, lawsuits. Estimated costs exceeded $200 million.
• Response. Target improved security protocols, adopted EMV chip card technology, and offered free credit monitoring to affected customers.
• Lesson learned. Keeping vendor access under control and monitoring third parties is essential to avoid breaches.

This incident highlights how a single compromised access point can trigger a domino effect, impacting an entire organization's ecosystem.

Equifax Data Breach

The Equifax data breach ranks among the most significant cyberattacks due to its scale and the sensitivity of the data stolen. In 2017, attackers exploited a vulnerability in Equifax’s web application framework, gaining access to the personal information of approximately 147 million people.

Key features of the Equifax breach:

• Data exposed. Social Security numbers, birth dates, addresses, and driver’s license numbers.
• Method. Unpatched vulnerability in the Apache Struts web application framework.
• Impact. Extensive identity theft risks and reputational damage. Costs related to the breach reached $1.4 billion.
• Response. Equifax offered victims free credit monitoring and identity theft protection services.
• Lesson learned. Timely application of security patches and robust vulnerability management are essential to mitigating cyber threats.

Equifax's failure to address known vulnerabilities is a prime example of how negligence can escalate small oversights into massive breaches.

How to Prevent Cyber Attacks

To prevent cyber attacks, companies need multiple layers of security, planning, and continuous improvements. Organizations must patch all vulnerabilities in their system, educate their workforce, and adopt advanced tools to detect and block them.

Main steps to prevent cyber attacks:

• Regular patching. Apply updates to close known vulnerabilities attackers may exploit.
• Multifactor authentication (MFA). Require multiple forms of verification to access accounts, reducing risks from compromised credentials.
• Encryption. Protect sensitive data at rest and in transit, ensuring it cannot be accessed if intercepted.
• Access controls. Limit user privileges based on roles, reducing exposure to sensitive information.
• Network segmentation. Isolate critical systems to contain potential breaches and minimize damage.
• Supply chain vetting. Evaluate third-party vendors to confirm they follow strong security practices against cyber attacks.

Encryption is essential for safeguarding sensitive data. Encrypting information both at rest and in transit ensures that, even if data is intercepted, attackers cannot read it. Supply chain vetting reduces risks. Verifying the security measures of third-party vendors and enforcing compliance standards prevents attackers from exploiting vulnerabilities in vendor systems to infiltrate your network.

Here are some advanced ways to detect and respond to cyber attacks:

• Threat intelligence feeds. Ensure awareness of emerging tactics, malicious actors, and potential risks.
• Behavior analytics tools. Monitor user activities for anomalies that might signal infiltration or misuse.
• Incident response drills. Conduct regular exercises to test and improve your team’s ability to respond quickly to cyber attack attempts.

Preventing cyber attacks is an ongoing process. Organizations that continuously assess their defenses, adopt best security practices, and maintain vigilance are the ones that stay ahead of cyber threats.

How to Detect Cyber Attacks

Cyber attackers often remain undetected for extended periods, quietly extracting valuable data. Let's explore ways to detect these hidden threats.

Cyber Attacks Detection Strategies

To effectively detect cyber attacks, companies need a combination of advanced tools and proactive approaches. The table below outlines the main strategies to identify and mitigate attacker activities:

Red Flags Indicating Possible Cyber Attack

Detecting cyber espionage and cyber attacks early requires attention to specific warning signs. The following table highlights common red flags to watch for:

Integrating Detection Methods

By combining advanced tools with proactive measures, organizations can significantly improve their chances of detecting cyber attacks and cyber espionage early. A practical approach involves layering multiple detection strategies to identify suspicious activities at various stages of an attack. For example, SIEM systems can flag unusual login patterns, while EDR tools analyze endpoint processes for signs of malicious behavior. Armed with this data, threat-hunting teams can dive deeper into anomalies for more thorough investigations.

Organizations should also integrate threat intelligence feeds to stay ahead of emerging attack techniques and known indicators of compromise (IOCs). For example, tracking connections to blacklisted domains or monitoring malware signatures linked to known attacker groups can provide valuable leads.

Here are some steps to improve integration:

• Correlate data from multiple sources. SIEM solutions pull together logs from firewalls, IDS/IPS, and endpoints, giving you a comprehensive view of potential threats.
• Automate responses to common alerts. Use automated playbooks to isolate suspicious endpoints or block malicious IP addresses immediately.
• Conduct regular threat-hunting exercises. Identify vulnerabilities by simulating real-world cyberattack scenarios.
• Customize alerts for specific risks. Tailor detection rules to address industry-specific threats, such as those targeting intellectual property in tech firms.

For example, a pharmaceutical company engaged in sensitive research could configure its SIEM to prioritize alerts for major data transfers or unauthorized access to research folders. Meanwhile, EDR tools would monitor employee devices for any signs of malware, ensuring swift action if a breach occurs.

Conclusion

Cyber attacks are constantly evolving, but each major breach offers insights on how to strengthen defenses. Looking at the biggest cyber attacks in history – like WannaCry, the Yahoo data breach, the PlayStation Network hack, NotPetya, and Operation Aurora – reinforces the importance of being proactive. This means regularly updating systems, training employees, and using advanced detection tools. These attacks show that while no organization is entirely immune, resilience is possible with the right strategies.