What is a data breach?

How data breaches happen

Breaches come from a mix of technical failures and human error. The most common causes include:

• Stolen or weak credentials. An attacker logs in with a phished, reused, or guessed password — the leading cause of breaches.
• Phishing and social engineering. An employee is tricked into handing over access or running malware.
• Unpatched vulnerabilities. Attackers exploit known flaws in software that wasn’t updated.
• Misconfigured systems. An exposed database or storage bucket left open to the internet with no password.
• Insider threats and lost devices. A malicious or careless insider, or a stolen laptop, leaks data.

What gets exposed — and why it matters

Not all breached data is equal. Email addresses and names fuel spam and phishing. Passwords — especially reused ones — enable credential stuffing and account takeover across every other site you use. Phone numbers feed SIM-swap reconnaissance. Dates of birth, addresses, and government IDs enable full identity theft. And because breach data is aggregated and resold, a single leak often ends up combined with older ones into a rich profile that outlives the original incident by years.

Real-world scale

Some of the largest breaches on record have exposed billions of records at once — email providers, social networks, hotel chains, credit bureaus, and identity-verification companies have all suffered incidents affecting hundreds of millions of people. The practical takeaway is simple: if you have used the internet for any length of time, some of your data is almost certainly in a breach corpus already. The question is not whether, but which accounts and how exposed — and that is something you can actually check.