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If you have an online account at a retailer like Amazon.com, you've probably run into such questions when opening an account or when trying to recover one of the dozens of passwords you juggle in your head. Online businesses everywhere have embraced the technique, which is called knowledge-based authentication.

Theoretically, the answers to these questions are so personal and obscure that knowing them proves you are you. Experts say, however, that the technology could end up helping hackers compromise your online accounts more easily.

Knowledge-based authentication doesn't replace user names and passwords; it's an extra layer of security on top of such schemes, since hackers who stumble across your log-in credentials won't easily figure out the name of your high-school sweetheart. Collecting log-in information and answers to secret questions from your computer requires keylogging software, making it harder for malicious hackers to triumph.

Phishers Get Close to Home

Jon Fisher, whose firm, Bharosa (acquired by Oracle last year), develops questions for companies to use, says knowledge-based authentication adds a step for account access. "Phishing both those pieces of information is fairly sophisticated."

But scammers have adapted, adding secret questions to their decoy pages, says Lance James, CTO of fraud research company Secure Science. Bank phishing sites may include their own fraudulent drop-down lists that capture people's answers, which bad guys can then use to hack real accounts.

Even when hackers don't resort to subterfuge, these nuggets of information can be easier targets than passwords. Mark Burnett, author of Hacking the Code, has observed that seemingly random questions such as "What was the make of your first car?" have a narrow list of answers--in the case of autos, 38 major makers--that hackers can use to try to break into an account, versus a vast multitude of password combinations.