Credit card numbers leaked

I have had three events over the last two months where my credit card details appear to have been leaked from my computer. The worrying thing is, apart from the fraudulent use of the card is that three sets of credit card details have been leaked. I have a new credit card ready to use but suspect that my Mac with ML 10.9.2 is dirty. What is the best way to clean and then protect against further presumably malware devils. Bearing in mind that I am also running windows on VMWare Fusion