RIP-OFF ALERT: Are you among the 70% of Americans who runs a balance on your credit cards? Your credit card issuer may be sneaking a rate change via a legalese statement that could show up with your next statement.

Here's the story: When interest rates started going up 3 years ago, issuers realized they could make more money by converting fixed-rate cards to variable-rate ones. So sure enough Clark started getting calls about that phenomenon.

Now they're doing the opposite thing as interest rates are declining. Dow Jones reports that Capital One has been doing this on new accounts only.

In theory, Clark has no problems with banks raising the rates on their credit cards to 1,000% on future purchases. Of course, it wouldn't be right to raise them retroactively on purchases you've already charged up.

If your issuer tries the latter tactic, you'll be hurting if you carry a balance. That's why you need to be in the 30% who don't carry revolving debt on their credit cards. Remember, the banks can't hurt you unless you give them permission to do so through your debt.