ETA. You CAN'T stop it from happening again. But you can make it a pain for the thief & buyers:
Have several accounts.
I have an input only acct (pay checks, etc) that NEVER gets used for purchases. I transfer money out into a bill pay acct, and a personal spending acct. my personal spending acct. only ever has small amts in it. I pretty much transfer on a daily basis. That way I never lose a LOT of money all in one swipe. I only deposit the ammt I'm paying on my bill, so that acct is nearly always empty (money for literally 60 seconds tops), and my daily spending acct, for a few hours.
Accts that have a few hundred in them at any given point sell for $20. Accts that have several thousand sell for around $100-$1000.
Credit Scores ALSO sell on the black market, btw. A good score costs more. Some people use good scores to set up their own cards (ID Theft) that they keep in good standing. Other people use good scores to slash and burn spend. It's part of why you want to keep an eye on your ACCOUNTS opened, even if your score is good / there isn't noticeable fraud.
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It is sooooo easy to get card numbers
Imprints, scanners (some people put devices on swipe stations that copy everything when you swipe), photos, listening (if you ever pay for anything over the phone), online, billing departments (medical, legal, utilities, creditors, etc.), receipts...
If you actually use your card to purchase anything... The numbers are the EASIEST thing to get. You don't even need any gear other than your eyes, but a camera will do it in a split second. Harder is the magnetic strip, but scanners get those, and you don't need the strip for online or over the phone purchases.
Sometimes it will be a recent purchase. Other times there will be a "hub" where someone collects thousands of card numbers, and the numbers get sold off for $20 a pop.
CC companies compare locations with other stolen numbers. So for criminal purchases it can be found out that Leah's Coffee on Dec 3 2011 was a grab location. (Meaning probably not an employee) Or that a lot of cards, slowly over time from XYZ store (probably an employee). Or, or, or, or. Won't help you much. But it helps the CC companies and police.