Nationwide Mutual Insurance Co. says someone attacked part of its computer network and likely stole personal information affecting more than 1.1 million people, according to The Associated Press.

The Columbus, Ohio-based company says that the Oct. 3 data breach occurred in a network also used by Allied Insurance. It has determined that the compromised information includes names, birth dates and Social Security and driver’s license numbers for customers and others who sought insurance quotes, the article says.

Nationwide is sending letters notifying those who are affected and is offering them free credit monitoring and identity theft protection for a year, AP reports. The insurer says it isn’t aware of the compromised information being misused.

Nationwide says the breach was discovered the day it happened and was contained. Law enforcement is investigating the breach.