I have been compromised once before with a monthly trickle on my bank account, and it had nothing to do with ecigs. As a government software engineer, ecommerce developer of many sites, and an administrator to several servers, I live by a couple of rules:
1. Antivirus and Malware protection always up to date.
For the comments that these are not being used to collect your credit card information, that is completely false. Many developers of malware these days are interested in trickle, potentially unnoticed bleeding of accounts. If 1000 PCs can be infected (which is extremely low for a true infection) at $10-$15 bleed per account, the author has effectively smuggled $10,000-$15,000 per month into their own account. Not so small when you figure most viruses and malware infect hundreds of thousands of PCs. Even if 50% of the users actually notice the charge, they have still made a huge chunk of change. Most of the time the offenders are overseas where it is harder to locate and prosecute (i.e. China has the largest hacking industry).
2. Don't store your credit card for future use.
Sure, most of the time it is encrypted and stored in some sort of a hash table, but if you really want to be secure, then you won't give the hacker something to look for. There is no way to verify that the vendor is ACTUALLY encrypting it, let alone the true security of their site (aside from trying to hack it).
3. Look at the site you are paying on, and look at the links you are clicking on to get there.
By now, most people should realize that somesite.something.paypal.com is legit whereas somesite.paypal.com.com or somesite.paypal.something.com is not (it must always end with [legit-site].[legit-extension]). Even if the second sites take you to the same place, they may be initiating scripts to capture your keystrokes as you are paying. This is why I rarely recommend clicking ANY links in your e-mail. If you need something from a site, go to that site directly.
4. Look for the little lock symbol (ensure the payment portion of the site is secure).
If you're really concerned, look at the certificate and make sure it belongs to a company you trust.
These tips should cover everything from the concerned to the extremely paranoid. I don't often check out certificates of trust myself, but it's not a bad idea if you're truly paranoid in regards to your security.