The largest data breach thus far this century involved all 3 billion accounts held by Yahoo, affecting hundreds of millions of users of Yahoo email, Yahoo Fantasy Sports, the Tumblr blogging and social-networking site and the Flickr photo-sharing site. While the Yahoo hackers stole email addresses and passwords, last year's breach of the Equifax credit-reporting agency involved the theft of far more consequential data: private financial information and Social Security numbers of 145.5 million Americans.

Sources: Taylor Armerding, “The 17 biggest data breaches of the 21st century,” CSO Online, International Data Group, Jan. 26, 2018,; Robert Hackett, “Equifax Underestimated by 2.5 Million the Potential Number of Breach Victims,” Fortune, Oct. 2, 2017,

Data for the graphic are as follows:

Year of Breach Company Breached Number of Accounts Compromised
2013 Yahoo 3 billion
2016 Adult Friend Finder 412.2 million
2017 Equifax 145.5 million
2014 eBay 145 million
2008 Heartland Payment Systems 134 million
2013 Target Stores 110 million
2006 TJX Companies 94 million
2015 Anthem 78.8 million
2011 Sony's PlayStation Network 77 million
2014 JPMorgan Chase 76 million

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