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Lessons from 5 of the Biggest Cybersecurity Breaches in History

Discover insights from major cyber security breaches. Understand recent cybersecurity breaches, lessons, and how to protect your organization against cybersecurity breaches effectively.

By Daniel Kelley

Lessons from 5 of the Biggest Cybersecurity Breaches in History

In this blog post, we will explore the 5 of the most biggest cybersecurity breaches in the history. These events exposed the personal details of millions, highlighting the growing challenges in protecting our digital lives. We've chosen these examples based on the scale of their impact, focusing only on instances where data was genuinely compromised. Join us as we explore what went wrong and the important lessons learned from these digital security breaches.

Covering the 5 Most Widespread Data Breaches


In today's data-driven world, data breaches can affect a huge number of individuals, reaching into the millions or even billions. As digital transformation continues to grow, data flow has increased, creating more opportunities for attackers to exploit the data dependencies that have become an essential part of our daily lives.

To ensure complete transparency, this list has been carefully created based on the number of affected users, exposed records, compromised accounts, and confirmed instances of hacks. It's important to mention that situations where developers found vulnerabilities but no actual data leaks happened, have been left out of this compilation.

Here, we present a comprehensive overview of the 5 most biggest data breaches in recent history. Explore the impact on affected parties, the entities responsible, and the responses of the companies involved in these breaches.

1. Yahoo (2013-2014) - 3 Billion User Accounts Breached

The Yahoo breach is widely recognized as one of the most significant cyberattacks, affecting a record-breaking number of people. It has the highest number of individuals impacted. The first attack occurred in 2013, with several more attacks happening in the following three years.

A group of Russian hackers specifically targeted Yahoo's database, utilizing various methods such as backdoors, stolen backups, and access cookies to retrieve records from all user accounts. These records contained personally identifiable information (PII) like names, email addresses, phone numbers, birth dates, passwords, calendars, and security questions.

Initially, Yahoo reported that data from approximately 1 billion accounts had been compromised. However, after Verizon acquired Yahoo in 2017, it was revealed that the actual number of affected records totaled around 3 billion accounts. Not only did Yahoo respond slowly to the breach, but the company also failed to disclose a separate incident in 2014 to its users. As a result, Yahoo faced a $35 million fine and became subject to a total of 41 class-action lawsuits.

2. LinkedIn (2021) - 700 Million User Profiles Scraped

In April 2021, a significant data leak incident impacted LinkedIn, the professional networking platform. This event affected over 700 million user accounts, which represented more than 90% of their user base at that time. The unauthorized extraction of data occurred by exploiting LinkedIn's application programming interface (API), which was a clear violation of their terms of service.

The compromised information included users' full names, email addresses, phone numbers, locations based on IP addresses, and any linked social media accounts. It's important to note that financial details and password credentials were not obtained during the data leak incident. However, security experts expressed concern regarding the potential risks of phishing scams and other social engineering cyber threats, given the large volume of emails and identities exposed, even without passwords being compromised.

Investigations revealed that multiple individuals had systematically leaked and aggregated public profile data over time. They then compiled and sold the combined information online. In response, LinkedIn took action by implementing new technical protection.

3. Facebook (2021) - 530 Million User Profiles Exposed

In April 2021, Facebook disclosed that the personal information of over 530 million users had been leaked online in a significant data breach event. The exposed details included full names, phone numbers, locations, birthdates, bios, and some email addresses of the users.

This data leakage was tied to a contact-importing feature that had enabled hackers to get massive amounts of profile information through automation. Notably, passwords and financial details were not obtained in the breach.

However, the huge amount of exposed personal data created significant risks for the security and privacy of hundreds of millions of users worldwide. With names, phone numbers, birthdates and other details now publicly accessible, impacted users faced increased dangers of spam calls, identity theft attempts, and other potential fraud.

Facebook claimed the vulnerability that allowed this data leak was patched in 2019. But the event highlighted ongoing concerns around the protection of user data, as such a massive leak of identities and contacts empowered criminals with data to potentially exploit users.

4. Marriott (2018) - 500 Million Guest Records Breached

In late 2018, the hotel giant Marriott International made headlines with one of the largest data breaches in history. This incident affected around 500 million guest records, leaving a significant impact. The breach originated in the Starwood hotel reservation system, which Marriott acquired in 2016.

Cybercriminals have had unauthorized access to the Starwood database since 2014, systematically extracting guest information. For a staggering 327 million individuals, the stolen data included sensitive details such as names, addresses, passport numbers, emails, phone numbers, birthdates, and reservation specifics. Credit card information was also compromised.

For the remaining guests, the breach resulted in the theft of more limited data, such as names and emails. Marriott identified the extensive breach as a result of malware that had been installed on the outdated Starwood system. The company faced widespread criticism for its failure to detect the intrusion and enhance security measures after acquiring Starwood.

5. Microsoft (2021) - 60,000 Worldwide Companies Affected

In January 2021, Microsoft made a significant revelation about a major breach that impacted over 30,000 organizations in the US and around 60,000 worldwide. This attack specifically targeted on-premise Microsoft Exchange servers, taking advantage of four zero-day vulnerabilities to gain unauthorized access to email accounts.

The hackers, later identified as a state-sponsored Chinese group known as Hafnium, capitalized on coding errors in Exchange to seize control of vulnerable systems. With just two conditions required - an internet connection and locally managed servers - the attackers could request data, deploy malware, create backdoors, and ultimately take over the servers.

This attack was acknowledged by the White House as one of the most extensive cyber-espionage campaigns ever conducted against the US government and private sector. It highlighted the risks associated with on-premise infrastructure and emphasised the criticality of prompt patching to mitigate vulnerabilities. Microsoft continues to urge customers to update their Exchange servers to the latest versions.

Enhancing Cybersecurity: Lessons from Recent Breaches

This table provides a concise summary of the scale, and key lessons learned from each breach:

BreachRecords LeakedLessons Learned
Yahoo3 billion user accounts- Security audits and system upgrades are critical. Hashing/salting passwords protects stolen data. Timely, transparent communication maintains trust.
LinkedIn700 million user profiles- Stronger API access controls and monitoring are needed. Review public data accessibility regularly.
Facebook530 million user profiles- Rigorous validation of external developers using data. Granular user consent controls for data access.
Marriott500 million guest records- Timely security evaluation after mergers & acquisitions. Encryption of sensitive data like passport details.
Microsoft60,000 companies affected-Regular patching and updates of on-premise software. Multi-factor authentication to flag unauthorized access. Isolate critical infrastructure from the public internet.

After carefully analyzing the table above, it becomes clear that every cybersecurity breach teaches us valuable lessons. These lessons cover a wide range of aspects, such as the importance of conducting regular security audits, enhancing API control measures, diligently validating third-party developers, conducting timely post-merger security evaluations, and ensuring consistent software updates.

These incidents collectively highlight the critical need for a comprehensive and proactive approach to cybersecurity.

4 Recent Cybersecurity Breaches


The online world provides us with great convenience and the ability to easily connect with others, but it also comes with potential security risks. Despite the strongest security measures, vulnerabilities still exist. Let's explore a few recent cybersecurity incidents that have captured public attention:

T-mobile Data Breach

In 2021, T-Mobile, a major player in the telecommunications field, experienced a serious security breach. This incident affected more than 50 million users, exposing sensitive information such as names, addresses, and social security numbers. It is a clear warning that even the biggest companies can be victims of cyberattacks.

Roblox Data Breach

Roblox, a popular gaming platform with a huge following among young players, also faced a data breach in 2022. This incident led to the exposure of numerous gamers' data, sparking worries about the security of online environments, particularly those used by children.

US Government Data Breach

2020 saw one of the most sophisticated cyberattacks in history. Multiple US government agencies, including those responsible for national security, were targeted. The scale and sophistication of the attack raised alarms worldwide, underscoring the evolving nature of cyber threats and the need for advanced defense mechanisms.

ChatGPT Data Leak

In a more recent incident in 2023, ChatGPT, a popular conversational AI platform, experienced a vulnerability that led to the exposure of sensitive user data. The incident highlighted the challenges in ensuring the security of emerging technologies and the importance of continuous monitoring and updating of security protocols.

How to Protect Your Organisation Against Cybersecurity Breaches

Compromised email accounts are a serious risk to your organization. With Keepnet's Threat Intelligence product, you can effortlessly monitor for exposed accounts that include your company's email accounts, staying one step ahead of cybercriminals.

Gain visibility into all leaked credentials associated with your business, empowering you to swiftly reset passwords and secure accounts.

By acting promptly, you can mitigate the risk across your organization, safeguarding your brand, employees, and customers against evolving email threats such as account takeovers and phishing attacks. It’s also important to educate your employees about cybersecurity threats so that they can protect themselves and your organization's data against cyber threats.

Watch the YouTube video below to see how Keepnet Labs’ Threat Intelligence tool operates to find your organization's leaked email data.



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tickEnsure your employees' passwords haven't been exposed in any known data breaches and act swiftly to secure them.
tickSee detailed breach information including date, time, password type, email address, and breach source to protect your company.
tickIncorporate with your existing security tools and SIEM (Security Information and Event Management) systems to automatically prevent breaches.
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