Some online stores are also not up to standard and could have spyware on their website, a few of the hosts in the US have bad spyware on their servers and its not uncommon to see people getting charges for payments they never made.
The trick is to use only sites with a high SSL security, look for the Green padlock in your address bar on anything you use a credit card on.
Some tips for online shopping:
1. Dont use public computers (ones at work are considered public)
2. Dont use public internet like the ones at a library, they have software in place to monitor everything you do therefore just a keylogger saving all your information.
3. Only shop from people offering services with a secure website, these can be seen from the Green padlock (some sites dont offer any security but offer all payments through paypal which is secure)
4. Use paypal for all online transactions (maybe the best option so that you never have to input details to a shop)
5. Use common sense, if the product looks too good to be true then yes it probably is.
6. Dont let the wife use your card online (learnt from that mistake, she now gets $100 on paypal a month to spend)
Just a few things to watch, there is not much you can do once your details are out there, filling out surveys with all your details can also cause headaches down the track with identity theft too.
What do you do if you feel a company may have your credit card details?
Report them to ASIC http://www.asic.gov.au/ and remove your details from their website as soon as possible.
Hope that helps, if you want some help feel free to pm me.