Hi kenj,
Thanks for the update on this very common problem in Brazil.
I'd like to mention that the banks here are not immune from the problem at all. Their machines are often tampered with because they are accessible at night. Outside of banks they usually aren't because they are either in shopping malls which are closed or they are in locations of high movement such as convenience stores and therefore not subject to being tampered with without being noticed.
A few more safety tips:
If you are using an ATM machine in any location more frequently than others, such as a specific bank branch, mall, etc., try to always use the very same machine and note down the machine's number which will be displayed both on the ATM itself and on your transaction stub or bank statement. Either memorize exactly what it looks like or take a photo of it with your cellular phone and if it appears in any way different from what you remember or from your photo don't use it. If it is in a bank bring that to the attention of the branch manager. Ask if they have made any repairs to or changed the machine and tell him or her you suspect it has had a skimmer faceplate added. These devices are quite sophisticated and can replicate the real machine's faceplate quite well.
Also if you begin a transaction and the machine will not complete the transaction and requests you phone a number to confirm or correct the error beware if it is not the 800 number of the bank, (You should get to know the 800 number of your bank)or if your bank has direct line telephones next to the ATM the message didn't instruct you to use that phone. Nobody at the bank service center will ever ask for your PIN number, if they do then you know you're being scammed. This is even more commonly done at night when the bank branch is closed so always return to the branch immediately when it is open and report the incident to someone in authority at the branch.
When using your credit/debit card for any purchases never let it out of your sight for a second. For example in a restaurant or at a gas station don't just give it to your waiter or the gas station attendant, go with them. You also need to beware since many of these hand-held devices are also skimmers that the owners of the establishment knows are cloning cards or have been replaced by organized crime groups posing as representatives of the bank or credit card company supposedly upgrading the equipment.
Cloning is almost impossible to avoid no matter what you do here in Brazil. The only real protection is to access your bank statement online as often as possible and monitor the activity very closely. At the first sign of any transaction you didn't make notify the bank immediately.
Some foreign banks actually monitor both your ATM and credit card activity and will actually phone you if they spot anything out of the ordinary. Sometimes they will even temporarily block your account if they have doubts until you contact them and confirm that a specific transaction was actually made by you or not. Some banks are now responding to skimming and cloning by installing fingerprint readers on their ATMs, but even this is going to be only partial protection for the bank customer.
Cheers, 
William James Woodward – Brazil Animator, °µÍø½ûÇø-blog Team