The compromised data includes 140,000 Social Security numbers, 1 million Canadian Social Insurance numbers and 80,000 bank account numbers, in addition to an undisclosed number of people's names, addresses, credit scores, credit limits, balances, and other information, according to Capital One and the US Department of Justice.
Paige Thompson, 33, was arrested in connection with the breach, the Justice Department said. The department alleges that Thompson "posted on the information sharing site GitHub about her theft of information from the servers storing Capital One data."
Thompson had previously worked as a tech company software engineer and was able to gain access by exploiting a misconfigured web application firewall.
"I sincerely apologize for the understandable worry this incident must be causing those affected and I am committed to making it right,"
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said Capital One CEO Richard Fairbank in a statement.
Capital One said it will notify people affected by the breach and will make free credit monitoring and identity protection available. The company expects to incur between $100 million and $150 million in costs related to the hack, including customer notifications, credit monitoring, tech costs and legal support due to the hack.