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You probably heard about the Target data breach that put the credit card numbers and personal information of millions of the retail giant's customers into the hands of cybercriminals in late 2013. But Target's security nightmare wasn't the worst data breach in history.
Here are the 10 worst data breaches in history — so far. (We haven't included the Home Depot breach disclosed in Sept. 2014 because no firm numbers for that breach have been provided.)
Heartland Payment Systems, 2008-2009: 130 million records compromised
In early 2009, this Princeton, New Jersey-based payment processor announced the largest data breach ever to affect an American company. Heartland's breach exposed information from approximately 130 million credit and debit cards to cybercriminals.
Malware planted on Heartland's network recorded card data as it arrived from retailers. Because the company processed payments for more than 250,000 businesses across the country, the impact was huge.
In 2010, Albert Gonzalez, the convicted mastermind behind the Heartlandbreach (as well as another huge breach), was sentenced to 20 years in prison — the longest sentence ever handed down for computer crime in a U.S. court.
Target Stores, 2013:110 million records compromised
In December 2013, retail giant Target confirmed that hackers had infected the company's payment-card readers, making off with approximately 40 million credit and debit card numbers that had been used at Target stores in the United States during the 2013 post-Thanksgiving shopping surge.
In January 2014, Target announced that the contact information — full names, addresses, email addresses and telephone numbers — of 70 million customers had also been compromised. Some of those customers probably also had credit-card data compromised in the earlier breach, but it's possible that as many as 110 million people were affected by the Target breaches.
Sony online entertainment services, 2011: 102 million records compromised
In April 2011, attackers whose identities are still unknown targeted the PlayStation Network that links Sony's home gaming consoles, as well as Sony Online Entertainment, which hosts massively multiplayer online PC games, and the Qriocity video- and music-streaming service.
Initially, Sony said that only the personal information of 78 million PlayStation Network users — login credentials, names, addresses, phone numbers and email addresses — had been exposed. But the tally of compromised accounts rose by 24.6 million when investigators discovered the attackers had also penetrated SOE and Qriocity. The credit-card data of approximately 23,400 SOE users in Europe was also stolen.
Following the initial breach disclosure, the PlayStation Network went dark worldwide for more than three weeks. In May 2011, Sony estimated its cleanup costs — which included fighting 65 class-action lawsuits brought against the company — at $171 million.
National Archive and Records Administration, 2008: 76 million records compromised
Not all data breaches are the result of criminal activity. In late 2008, a hard drive at the National Archive and Records Administration (NARA) stopped working. It held the names, contact information and Social Security numbers of 76 million U.S. military veterans.
Instead of being destroyed on-site, the drive was sent for repair to a government contractor, which determined the drive could not be fixed — so it was sent it out to be scrapped. It is not clear whether the drive was actually destroyed.
Following complaints by an IT manager at NARA, an investigation was launched, and NARA changed its policies to destroy all malfunctioning storage media containing sensitive personal information.
"NARA does not believe that a breach of PII [personally identifiable information] occurred, and therefore does not believe that notification [of the affected veterans] is necessary or appropriate at this time," the agency told Wired News in 2009.
Epsilon, 2011: 60 million to 250 million records compromised
In March 2011, the Texas-based marketing firm Epsilon, which handled email communications for more than 2,500 clients worldwide — including seven Fortune 10 companies — announced that databases pertaining to about 50 Epsilon clients had been stolen.
Email addresses of at least 60 million customers ended up in the hands of cybercriminals, and more than a dozen major retailers, banks, hotels and other companies were affected, including Best Buy, JPMorgan Chase, Capital One Bank and Verizon.
Epsilon could not confirm exactly how many individuals were affected. Conservative estimates put the number of email addresses stolen at 60 million, but according to the Privacy Rights Clearinghouse, a San Diego-based nonprofit advocacy group, the number may have been as high as 250 million.
Evernote, 2013:More than 50 million records compromised
In March 2013, users of the note-taking and archiving service Evernote learned that their email addresses, usernames and encrypted passwords had been exposed by a security breach. No financial data was stolen, and the company confirmed that none of the user-generated content on its servers had been compromised.
However, as had been the case for those affected by Epsilon's 2011 breach, Evernote users who had their usernames and email addresses stolen were vulnerable to spam emails and phishing campaigns — some of which pretended to be password-reset emails coming from Evernote itself.
Living Social, 2013: More than 50 million records compromised
In April 2013, Living Social, a daily-deals site partly owned by Amazon, announced that the names, email addresses, birth dates and encrypted passwords of more than 50 million customers worldwide had been stolen by hackers. Twenty million Living Social customers whose information was stored on servers in Asia were not affected.
TJX Companies Inc., 2006-2007: 46 million records compromised
When it was discovered in 2007, the TJX data breach was the biggest theft of consumer data ever in the United States, affecting the parent company of several major retail brands, including Marshalls, T.J. Maxx and HomeGoods. Approximately 45.6 million credit and debit card numbers were stolen over an 18-month period.
About 450,000 TJX customers also had their personally identifiable information stolen, including driver's license numbers. The breach ultimately cost the Framingham, Massachusetts-based company $256 million.
The TJX hackers included Albert Gonzalez, who was cooperating with law-enforcement investigations into earlier data thefts when he took part in both the TJX breach and the even larger Heartland Payment Systems attack two years later.
Adobe Systems, 2013: At least 41 million records compromised
In October 2013, the American graphics-software giant Adobe Systemsrevealed that user email addresses, encrypted passwords, password hints and, in some cases, usernames pertaining to 150 million accounts had been stolen from its servers.
An Adobe spokeswoman told security blogger Brian Krebs that only 38 million of those accounts had been active. The remaining ones, she said, were invalid, duplicate or test accounts. Subsequent announcements by Adobe revealed that some 3 million encrypted credit card records had also been stolen.
CardSystems Solutions, 2005: More than 40 million records compromised
When this breach was disclosed in June 2005, CardSystems Solutions of Tucson, Arizona, was the card-payment processor of choice for more than 100,000 small U.S. companies, and processed $15 billion in transactions annually.
Malicious hackers took advantage of CardSystems' lax security measures, gaining access to the names, account numbers and verification codes of more than 40 million cardholders. A probe found that CardSystems had failed to comply with Payment Card Industry security standards, and the company was forced into acquisition in late 2005.