Biggest Data Breaches in History

In the digital era, data breaches are more common and impactful than most people imagine. When attackers access personal information—names, emails, passwords, social security numbers, or payment details—the consequences ripple from individuals to entire industries. This article examines the biggest data breaches in history, what made them so damaging, and what changes they forced in cybersecurity practices and consumer safety.

Why some breaches become historical milestones

We measure scale by records affected, but the cost isn’t just a number. It includes remediation expenses, regulatory penalties, stock impact, and the erosion of trust that follows. The breaches described here illustrate a pattern: attackers leverage weak links—outdated software, careless access controls, or third-party gaps—and once inside, they often move laterally across systems to siphon sensitive data.

Notable incidents that shaped the landscape

Yahoo (2013–2014)

At one point the breach is considered to have affected more than 3 billion accounts, making it one of the largest ever discovered. The attack compromised names, email addresses, hashed passwords, and security questions. The long span between the intrusion and discovery allowed attackers to harvest data gradually, with consequences that reverberated for years. The incident played a part in Yahoo’s reduced sale price to Verizon and pushed banks and services to rethink credential storage and two-factor authentication.

Equifax (2017)

The Equifax breach exposed sensitive information for about 147 million people, including Social Security numbers and birth dates. The breach occurred due to a known Apache Struts vulnerability that went unpatched for weeks. Beyond the immediate privacy damage, it sparked sweeping regulatory scrutiny, massive class actions, and a lasting reminder that consumer data in credit reporting can be a national security risk.

Marriott / Starwood (2014–2018)

In what investigators described as a prolonged intrusion, Marriott announced a breach affecting roughly 500 million guests. The exposed data included contact details, travel histories, and, in some cases, passport numbers. The incident underscored the risk of long-tail exposure in supply chain ecosystems and forced the hospitality industry to rethink data segmentation, third-party access, and monitoring across global networks.

Target (2013)

Target disclosed that about 110 million customer records were compromised during the holiday shopping season. Payment card numbers and contact information were among the data stolen through an attack that began with a third-party vendor credential. The breach led to a multi-year security overhaul at large retailers and a push for better point-of-sale protections and vendor risk management.

eBay (2014)

Approximately 145 million eBay accounts were affected when attackers gained access through employee compromised credentials and misused them to access user databases. The breach forced eBay to reset passwords, enhance authentication, and accelerate efforts to segment data so that a single stolen credential could not lead to broad access again.

MyFitnessPal (2018)

Under Armour reported that its MyFitnessPal app was breached, exposing about 150 million user accounts. The attackers accessed usernames, email addresses, and hashed passwords, depending on the data present in the compromised database. The incident highlighted the importance of securing consumer health and wellness platforms that hold highly personal information.

Capital One (2019)

Capital One disclosed a breach affecting more than 100 million people in the United States and several million in Canada. A former employee exploited a misconfigured firewall to access data including names, addresses, phone numbers, and some credit scores. The breach accelerated reviews of cloud configurations and moved many banks to tighten monitoring of third-party access and internal misuse.

Heartland Payment Systems (2008)

Heartland faced one of the earliest large-scale payment-card breaches, involving around 130 million credit and debit card numbers. The attackers installed malware on payment processing networks to harvest data, highlighting how point-of-sale ecosystems could be an attractive vector for perpetrators and leading to industry-wide enhancements in transaction handling and encryption standards.

TJX Companies (2007)

The TJX breach affected tens of millions of cardholders whose data was compromised through weak store network security. The incident drew attention to how even retailers with physical store operations must invest in modern network segmentation, robust monitoring, and rapid incident response to deter prolonged access by attackers.

Anthem (2015)

Health insurer Anthem reported a breach impacting about 78 million individuals. The stolen data included names, dates of birth, Social Security numbers, and medical IDs. The breach underscored the sensitivity of health data and led to a wave of enhanced data-protection requirements across the health sector, including more aggressive breach notification and credit monitoring offerings for patients.

LinkedIn (2012) and related disclosures

The LinkedIn compromise of 2012 affected hundreds of millions of accounts, with ongoing revelations about additional data exposures surfacing in subsequent years. LinkedIn’s breach illustrated how credential leaks can fuel widespread phishing and reuse attacks, pushing tech firms to invest more in password hygiene and breach response.

Uber (2016)

Uber disclosed a breach affecting around 57 million riders and drivers worldwide. The data included names, email addresses, and phone numbers of users, while driver license data was not always affected. The incident amplified discussions about how ride-hailing platforms store and share data, and what governance is needed for third-party vendors and incident sharing with users.

Across these cases, several themes repeat: attackers leverage third-party access, chronic underinvestment in basic controls, and delays in identifying intrusions. The resulting financial penalties, regulatory scrutiny, and lasting reputational damage are a cautionary tale for organizations large and small.

What these breaches teach us and how to protect yourself

• Use unique passwords across sites and services, and enable two-factor authentication wherever possible.
• Monitor your accounts for unusual activity and set up breach alerts from reputable services.
• Be cautious with email links and attachments, especially following a security incident that involves a company you use.
• Consider credit freezes or fraud alerts if your personal information has appeared in a breach.
• Prefer services that encrypt data at rest and in transit, and demand transparency from vendors about their security practices.
• Regularly update software, patch vulnerabilities, and audit third-party access to networks and data stores.

Why history matters for the future of security

The biggest data breaches in history did not just leak data; they exposed the fragility of systems we rely on daily. They shifted regulatory landscapes, reshaped consumer expectations, and forced companies to rethink how they monitor, store, and protect sensitive information. The cadence of breaches has grown louder, but so have the defenses: stronger encryption, demand for zero-trust architectures, and more rigorous incident response governance. As long as valuable data exists, so will attackers. The objective for individuals and organizations is to reduce risk, shorten the time between breach and detection, and build a culture where security is part of everyday decision making rather than an afterthought.