In the Northern California Breach, the card numbers were used in signature transactions versus PIN (Personal identification number) transactions. When ATM skimming is accomplished, the criminals steal not only the card number, but the PIN, also.
They are then able to use the card at any ATM.
Automatic teller machine (ATM) skimming is accomplished by attaching devices to existing ATM Machines, or via the use of hidden cameras/encoding devices in retailers that accept ATM transactions.
ATM skimming has been prevalent overseas for a few years, but is starting to show up in North America. Recently, skimming devices have been discovered on ATM machines in California, Oregon and Washington. This is why the two activities are probably being compared.
Awhile back, I did a post: ATM Machines That Clone Your Card. Included are some handy pictures of what a machine looks like after it has been compromised and tips on how to avoid becoming a victim.
There are similarities to both activities, but there are differences, also.
In the "ATM Skimming" cases, devices are being attached to existing ATM machines, which not only record the card numbers, but PIN numbers, also. The victims in the recent cases seem to span the entire West coast.
Interestingly enough, a few months ago, I did a post, which noted ATM skimming activity on the East coast:
Get a Quick $20.00 and GO BROKE!