Verizon has confirmed the personal information of 6 million customers was recently leaked online.
A cyber-security company named Upguard uncovered the issue, saying it was caused by "human error."
Upguard alerted Verizon on June 13, but the security hole was not closed until June 22.
Verizon said no loss or theft of customer information occurred.
Upguard is still advising Verizon customers to update their pin codes and never use the same one twice.