Well... I guess I should have been a little more careful but today I learned a valuable lesson in using ATMs. It's best to use one at a bank or trustworthy location.
I arrived this evening at Koh Samui airport and in need of Thai Baht, I went to a Siam Commercial bank ATM that was next to a bunch of other ATMs at the meeting point area after you come out of Arrivals.
I put in my US ATM card which the ATM recognized and accepted. Thankfully, the ATM also gave back your card after you've swiped it - like most modern ATMs. Went through all the usual withdrawal steps and just before it was to spit out the money, the ATM and all the ATMs next to it lost power for a brief 2-3 seconds.
After that, I knew that I've been had. It was too coincidental that a brief power outage (as it someone pulled the plug and then plugged it back in immediately) would happen just as it was going to give me the money. The ATMs are in a very public area and what you do can easily be observed. There were a few guys standing by the taxi desk and they look pretty interested in what I was doing - but of course, there's not much I can do nor were there help around.
When the ATM regained power, the internal system rebooted itself (it's a Windows OS) and in a few minutes, it was ready to be used again by another unsuspecting fool like me. And no, it didn't start sending out any money and so, I don't know exactly what the scam intentions are i.e. was it to collect my card number and PIN, or for the ATM machine to keep the money that it didn't give out or is there a way for someone else to collect the cash later... I don't know.
I went online and checked my bank account, and unfortunately, $350 USD (equivalent to 10,000 Thai Baht) was withdrawn at that ATM. I contacted my bank to freeze the account and I'm hoping I can resolve the issue with Siam Commercial bank on Monday when they open - since it looks like their ATM kept my 10K baht.
Lesson learned. Be forewarned!