I just went through this stuff after an identity theft incident. While locking my Equifax file, I learned something surprising:

Locking your Equifax credit report prevents access by potential creditors and lenders, but there are exceptions. ... Companies that wish to make pre-approved offers of credit or insurance to you ...

Equifax maintains consumers’ credit reports and provides information to certain customers, including credit card companies and lenders, so that they may offer pre-approved offers to consumers as permitted by law. Consumers that prefer not to receive such offers should visit www.optoutprescreen.com, or call toll free at 888-5-OPT OUT (or 888-567-8688).

So I'd really encourage everyone to do that opt out thing, too.