Top 10 Biggest Cybersecurity Breaches of All Time

The 2013 Yahoo breach affected 3 billion accounts, making it the largest breach by number of compromised accounts.

Personal identifiable information (PII) such as names, email addresses, passwords, and financial data is most commonly targeted, though some breaches also exposed intellectual property or trade secrets.

Attackers often exploit weak passwords, phishing emails, unpatched software vulnerabilities, or insider threats to gain initial access.

Companies face financial losses, legal penalties, reputational damage, loss of customer trust, and often must implement costly security upgrades and compliance changes.