We hear about them all the time in the news, a credit card skimmer was found on this ATM or at this bank. The above video shows just how quickly one can be installed onto a credit card reader.
After seeing this video I've gotten into the habit of giving a tug on any card slot before I use it. It doesn't have to be a herculean pull, just tugging on the area where the card goes will give you an idea if everything is legit or if someone is trying to steal your info. Some skimmers even have mini cameras so they can see what the PIN number is typed in with the card. Be on the lookout and be sure to check the credit card readers so you don't become a victim!