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COLUMBUS, Ohio-- Nationwide Mutual Insurance Co. says someone attacked part of its computer network and likely stole personal information in a data breach that affects more than 1.1 million people.

The Columbus, Ohio-based company says the Oct. 3 breach occurred in a network also used by Allied Insurance.

It has determined the compromised information included names, birth dates and Social Security and driver's license numbers for customers and others who sought insurance quotes.

Nationwide is sending letters notifying those affected and is offering them free credit monitoring and identity theft protection for a year.

The insurer says it isn't aware of the compromised information being misused. The company says the breach was discovered the day it happened and was contained. It's under investigation by law enforcement.