My girlfriend and I stayed from Wed-Sun night of Semana Santa. She logged in to her 24 hour banking yest and found over 700 euro had been taken from her debit card. Then she logged in today and found the same thing had happened with her credit card!
At first we assumed it was the ATM near the Pana dock in San Pedro. She tried the machine twice on Sunday and it didn't allow us to withdraw money. But now that we see the details of the credit card were also copied (and she hasn't used the card anywhere for over a month). It seems most likely that someone went into one of the rooms where we were staying and copied the cards. The purchases were made around the Lago Atitlan area.
At the moment we don't want to say where this may have happened, because we stayed in two different places over the five nights. However, one place insisted we stay 2 nights and seemed quite eager to clean our room while we were out during the day. If anybody else has had a similar experience, please post and let us know.
As an aside, she left the cards in the room for security reasons - we were walking in areas around the lake where there apparently have been robberies in the past (we found it perfectly safe) so we wanted to carry as little as possible. So I don't know what the answer is for keeping your cards secure.
On a brighter note, even though she has no cards now, the bank is refunding the money, as they should.