American Airlines discovered it was breached after receiving reports of employee email accounts being used in phishing attacks.
Last week, the airline started informing some of its customers that their personal data was likely compromised in a data breach identified in early July.
As part of the incident, unknown threat actors compromised the email accounts of multiple American Airlines employees, which allowed them to access customer data in those accounts, the company said in the notification letters sent to the impacted customers.
In a notification letter sample filed with the New Hampshire Attorney General’s Office, the airline also disclosed the fact that the data breach was not discovered until after it received complaints of phishing emails being sent from its employee email accounts.
According to the company, the attackers might have also used the compromised accounts to access files stored on an employee SharePoint site.
American Airlines also notes that the attackers accessed the compromised mailboxes using the IMAP protocol, which could have allowed them to sync the contents of those mailboxes to another device.
“American has no reason to believe that syncing the contents of the mailboxes was the purpose of the access. Based on the facts, it appears the unauthorized actor was using IMAP protocol as means to access the mailboxes and send phishing emails,” the notification letter reads.
The airline told US authorities that the breach has impacted roughly 1,700 customers and employees.
The company notes that “the number of documents that contained personal information was small and it would have taken the unauthorized actor significant time and resources to locate the personal information on the mailboxes.”
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