Yahoo's massive data breach could affect hundreds of millions of users. USA TODAY
SAN FRANCISCO —  Yahoo's announcement 500 million accounts had been breached, possibly by a state-sponsored attacker, looks to give it the unwanted title as largest data breach ever, by users affected.
To ascend to the top of the list, it had to beat out other big consumer breaches, from LinkedIn to AshleyMadison. For purposes of this ranking, we did not include hacks with under 1 million users, such as the Sony Pictures Entertainment breach, which was expansive in terms of the volume of personal information stolen but was largely contained to Sony employees.

USA TODAY
500 million Yahoo accounts breached
Yahoo! 500 million, September 2016
MySpace 360 million May 2016
LinkedIn 100 million, May 2016
Scottrade, 4.6 million, October 2015
T-Mobile (via Experian), 15 million, October 2015
Ashley Madison, 32 million, August 2015
Anthem 80 million, February 2015
Office of Personnel Management, 21.5 million, July 2015
UCLA Health 4.5 million, July 2015
Home Depot, 53 million, September 2014
EBay 145 million, May 2014
Target, 110 million, November 2013
JP Morgan Chase, 83 million, October 2013
Sony PlayStation Network, 77 million, April 2011
TJ Maxx, 45.7 million 2007
AOL, 92 million, October 2007
Source: USA TODAY Research