One important distinction to make is determining whether the card was compromised or rather it is frozen by the credit card issuer. Credit card processors will often lump gun stores in with other businesses such as gambling sites which they deem to be "high risk". If they note you making a purchase on one of these "high risk" sites they will sometimes freeze your card until given the approval from the card owner that the purchase is legit.
Now of course in the cases described in some of the above posts it seems the cards were in fact compromised and not just frozen. To that end it would be nearly impossible to detect how and where each card was compromised and whether or not each case rooted back to our site. What I can do is outline how cards are processed through our website. When it comes to orders made through our online shopping cart we as a company do not have access to your individual credit card numbers or info. This information is handled by the gateway and the card processor. In order to be compromised through our site it would in fact have to be compromised at that level. Our website is hosted by Big Commerce which is a large company with thousands of e commerce sites that they host around the world. Every part of our site is hosted by them and no portion of our site either front or back end is local to our computers. BigCommerce is fully PCI compliant. Our own local IP is also fully PCI compliant and we run professional grade antivirus software continually. In order to have our terminals in store, our payment processor remotely runs a scan against our public IP looking for any issues.
Now of course we can't say for sure that cards haven't been compromised while using our site as there is risk anytime you use your card that something may happen, however it is very unlikely to be the case that card info was compromised on our site. There are numerous safeguards in place and we would be alerted through the numerous channels at the first sign of something not being right. I hope this has helped to alleviate any concerns.
Ed.