I was wondering about this too. Like, I never signed up for them, but apparently their site says I might have been affected. CreditKarma or other credit score companies apparently share user data to these agencies.
Their announcement says social security, addresses and names have been stolen, this is really worse, this data is enough to do ton of things.
CreditKarma doesn't give info to Equifax, it gets info from Equifax.
The credit agencies (of which equifax is one of 3) get their info from credit card companies and other financial institutions. If you've ever signed up for a credit card or gotten a mortgage or car loan the information from that transaction was sent to the credit reporting agencies. That's how they get data to make their determination of how credit worthy you are.
Their announcement says social security, addresses and names have been stolen, this is really worse, this data is enough to do ton of things.