(MONEY Magazine) – High-tech thieves are getting better at defrauding users of ATMs -- meaning you need to be more vigilant than ever about guarding the privacy of your transactions. In the latest case, the Secret Service arrested two men in June who allegedly helped place a phony ATM in a Connecticut shopping center. Prosecutors said Alan Pace of New York City and Gerald Greenfield of Tucson were part of a ring that wheeled the bogus machine into a Manchester mall on April 24 and then wheeled it out 15 days later after it had captured the card data -- including personal identification numbers, or PINs -- from hundreds of unsuspecting shoppers. (The machine would record the information and then return the card, saying it couldn't process the transaction.) The crooks then created counterfeit ATM cards to withdraw more than $100,000 from legitimate machines. The Connecticut case was not the first, though. The Secret Service is looking for another gang that made off with more than $200,000 earlier this year by videotaping ATM customers in Los Angeles with a concealed camera. The bandits watched the video to learn people's PIN numbers, and got their account and card numbers from ATM slips discarded at the machine. And when agents busted some credit-card counterfeiters in New York City last November, they found videotapes of ATM customers and discarded ATM slips among their paraphernalia. Granted, most of the $18 million lost to ATM fraud each year stems from such causes as people writing their PIN number on a card that is later stolen. And federal law limits your loss to $50 if you notify the bank within two business days. Nevertheless, all bank customers pay for fraud in the form of higher fees. Until ATM security becomes foolproof, here are some commonsense rules to observe: Don't write your PIN anywhere a thief might find it. Conceal the keypad or touch screen with your body when entering your PIN. Take your ATM receipt with you when you leave. Finally, make sure the ATM is permanently installed. Incredibly, no one realized the Connecticut machine was fake, though it was sitting on wheels.