Quick: What was the colour and make of your firstborn’s second car? In what year did your father remarry? What were your mortgage payments in 1993? Better get used to questions like this. As a new line of defence against identity thieves, a rapidly growing industry of data brokers is rushing to the rescue, aggregating public and private databases, and then selling that information in the form of multiple-choice questions to companies eager to trip up impersonators.

Instead of using information you give to your credit-card company — your pet’s name, or your favorite movie — this type of verification makes use of information about you gleaned without your knowledge from public databases. London-based credit agency Experian, for instance, culls information from hundreds of sources — including courthouse records, electoral registries and BT — to supply its 200-plus British clients with so-called challenge questions. If a customer arouses suspicion, the credit-card company sends the name to Experian and gets back, seconds later, a list of questions that can be put to the customer to verify his identity.

Although Experian is developing similar services in other European countries, this kind of “out of wallet” authentication — so named because answers to the questions are rarely found in written form — is growing most rapidly in the United States, where privacy laws are less strict. For each challenge, Experian charges a dollar or two, depending on volume. Jim Lound, Experian’s product director, says the alternative — requiring applicants to submit additional documents—is even more expensive.

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