Credit card companies are lowering credit limits and even closing the accounts of some of their best customers.

It seems an idiotic way to treat cardholders who have always paid their bills on time.

But they weren't chosen at random for this surprising treatment.

Credit card companies are using data profiling, which looks at everything from where customers shop, work and live to predict whether they'll be able to keep paying their bills a few months from now.

"Data profiling is looking at your history in an attempt to predict your future," says Jim Randel, author of the book The Skinny on Credit Cards. "What credit card companies are worried about is that you're going to pay late or default. So they look for red flags."

Thanks to the recession, lots of cardholders are failing to keep up with even the minimum payments on their cards.

With the unemployment rate approaching 10%, something like 6.5% of all credit card accounts are at least 30 days late.

Bank of America says it may have to write off nearly 14% of the total balance on its credit cards. American Express and Citigroup say 10% of what they're owed may never be repaid.

As a result, the cards are trying to figure out who the recession's next victims might be -- and cut off their credit.

Exactly what they're looking at is difficult to know because credit card issuers say little about the computer programs they use to comb through your life.

But we've seen reports of credit limits being dramatically reduced -- from $40,000 to $4,500, in one case -- based on where customers live and what they do for a living.

In those instances, card companies seemed to be targeting customers who lived in states and worked in industries (such as construction and banking) that have been particularly hard hit by the recession and financial crisis.

American Express has told cardholders that their credit lines are being cut based on where they shop.

Cardholder Kevin Johnson, for example, made it a personal mission to figure out where that might be after his credit limit was reduced by $7,000 because, he was told, "other customers who have used their cards where you recently shopped have a poor repayment history with American Express."

Johnson thinks it's because he used his card at Walmart. But American Express wouldn't tell him whether that was the case.

"I would like them to restore the credit," Johnson told ABC's Good Morning America. "But more than that, I would like them to become more transparent. I don't think anyone would agree to being discriminated against based on where they shop."

Financial experts have some other ideas about what the credit card companies might be looking for, such as using your card:

• At a bar. If you're drinking, maybe you're worried about being laid off.
• At a marriage counselor. If divorce is ahead, you could become a financial wreck.
• To pay for car repairs. If you have to fix rather than replace your ride, you must not have enough money for a new one.
• To check your balance at 1 a.m. Are financial worries keeping you up at night?

What can you do?

Not a lot.

You might make a point of paying cash at bars or writing a check to your counselor. But "to try to change your behavior too much to try to outsmart the system doesn't make a lot of sense," Randel says.

And you certainly can't do anything about the campaign by banks and credit card companies to reduce credit limits.

According to Meredith Whitney, the Wall Street analyst who became famous for predicting the banking crisis, our total available credit will be cut by more than half.

In an opinion piece she wrote for the Wall Street Journal, Whitney says consumers have used about $800 billion of the $5 trillion available credit on their accounts.

But the amount of available credit was reduced by $500 billion in the final three months of 2008. By the end of 2010, Whitney expects the amount of credit available to consumers on their cards will be down to about $2.3 trillion.

By Jen A. Miller

Interest.com Contributing Editor