The security issue was uncovered by research from cybersecurity firm UpGuard.
They say it was caused by a misconfigured security setting on a cloud server due to "human error."
The error made customer phone numbers, names, and some PIN codes publicly available online.
PIN codes are used to confirm the identity of people who call for customer service.
According to Verizon, no loss or theft of customer information occurred.
UpGuard initially said the error could impact up to 14 million accounts.
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