Epsilon

Epsilon—the world’s largest permission-based email marketing company suffered a massive data breach incident in April of 2011 where the names and addresses of 60 million users were stolen.

An unauthorized entry got into Epsilon’s email system and breached the mails and names of around 2% of their clients.

Companies like Walgreens, BestBuy, CitiGroup, JPMorgan, Capital One and others were all affected indirectly.

Source: https://www.proofpoint.com/us/blog/insider-threat-management/throwback-hack-epsilon-email-breach-2011

"id": "EPS153827123",
"linkid": "epsilon",
"type": "Breach",
"date": "04/2011",
"severity": "100",
"impact": "4",
"explanation": "Attack with significant impact with customers data leaks"