May 29, 2026, 7:06 p.m.

Equifax Data Breach: How 147 Million Social Security Numbers Were Stolen?

The Equifax data breach of 2017 went down in history as one of the largest and most costly cybersecurity incidents ever recorded. This breach at Equifax, one of the largest credit reporting agencies in the United States, resulted in the theft of sensitive data belonging to 147 million people. Even worse, the fundamental cause of this disaster was the failure to timely patch a known security vulnerability and the neglect of basic security measures.

In this blog post, we will examine in detail how the Equifax data breach occurred, what chain of errors led to this catastrophe, and the lessons that must be learned from this incident in terms of corporate cybersecurity. We will particularly focus on what organizations in Turkey can learn from this case.

Anatomy of the Incident: Apache Struts Vulnerability (CVE-2017-5638)

The root cause of the Equifax data breach was a critical security vulnerability in the Apache Struts framework used in the company's web applications. This vulnerability, coded as CVE-2017-5638, was publicly disclosed in March 2017 and allowed Remote Code Execution (RCE) in Apache Struts' Jakarta Multipart parser component.

This vulnerability was particularly dangerous because it allowed attackers to execute arbitrary commands on the target system by sending specially crafted HTTP requests. When the security patch was released by the Apache Struts community in March 2017, cybersecurity teams around the world began emergency patching efforts. However, this was not the case for Equifax.

Critical Two-Month Delay

Equifax's biggest mistake was the incredible delay in implementing the security patch. Despite the patch being released in March 2017, the company only updated its systems in late May 2017. This two-month delay gave attackers sufficient time to infiltrate the company's network and steal sensitive data.

The problem wasn't just the delay; serious coordination deficiencies in Equifax's patch management processes also emerged. Although the company's security team reported that the patch needed to be applied, it was discovered that not all systems were scanned and some critical servers were overlooked.

Scale of the Data Breach and Stolen Information

The scope of information stolen in the Equifax data breach was truly shocking. The attackers remained undetected in Equifax systems for approximately two and a half months, from mid-May to July 2017, during which they exfiltrated massive amounts of sensitive data.

Stolen Data

• Social Security Numbers (SSN) of 147 million American citizens: The most critical personal identifier used for authentication and credit transactions in the US
• Names and birth dates: Basic identity information
• Home addresses: Physical location information
• Credit card numbers of 209,000 individuals: Direct financial information
• Digital copies of identification documents of 182,000 individuals: Documents such as driver's license and passport copies

Data Encryption Failure: The Price of Negligence

Another critical error that made the Equifax case even more severe was that most of the stolen data was stored unencrypted. The principle of "data encryption," one of the most fundamental rules of modern cybersecurity principles, was not adequately implemented by Equifax.

If the data had been protected with strong encryption algorithms, even if attackers accessed the database, they would have needed additional resources and time to make this information usable. However, unencrypted data was directly readable and usable by the attackers.

$700 Million Settlement and Legal Consequences

The financial cost of the Equifax data breach reached astronomical proportions. In 2019, as a result of an agreement with the U.S. Federal Trade Commission (FTC), the Consumer Financial Protection Bureau (CFPB), and 50 states, Equifax agreed to pay approximately $700 million in total compensation.

Distribution of the Settlement

• $425 million: Consumer compensation fund for victims
• $175 million: Penalties to states and territories
• $100 million: Civil monetary penalties to the CFPB

Beyond this, Equifax's costs for upgrading cybersecurity infrastructure, improving monitoring systems, and hiring new security personnel reached billions of dollars. The damage to the company's brand reputation was immeasurable.

Lessons for Turkish Companies

The Equifax case contains critical lessons not only for America but also for organizations in Turkey. Considering KVKK (Personal Data Protection Law) and increasing cyber threats, the lessons Turkish companies should learn from this incident are of vital importance.

1. Patch Management Is Critically Important

Equifax's biggest mistake was not patching a known security vulnerability in time. Similar risks exist for Turkish companies. Especially organizations in critical infrastructure and the financial sector should automate and prioritize their patch management processes.

Recommendations:

• Policy to apply critical security patches within 24-48 hours
• Establishment of automated vulnerability scanning systems
• Creation of clear responsibility matrix for patch management
• Assessment of patch impacts in test environments

2. Data Encryption Is Non-Negotiable

Equifax's unencrypted data storage error is an important warning for Turkish companies from a KVKK perspective. All organizations operating in Turkey must protect the personal data they collect with strong encryption methods both during storage and transmission.

What Must Be Implemented:

• Encryption of sensitive data with strong algorithms such as AES-256
• Database-level encryption