What Size Magnet Can ERASE a Credit Card?

I've read that two cards placed stripe to stripe can destroy one another. Also, chip cards may be secure, but they are just as easily stolen. Try the chip 3 times at almost any pin pad and you can slide the card, then you can just press enter when asked for a pin to run a debit card as credit. From working in a grocery store I see this all the time and at the cost of angering a potentially legit customer, we let it go. You can thank good customer service for most retail cc fraud.