Some data brokers sell truncated SSNs, with either the first five or the last four numbers visible to the purchaser. That's important, because there are many ways to determine the last four digits of someone's Social Security number. In one example, the researchers said, they can uncover a Delaware resident's 9-digit SSN within 10 guesses about 5 percent of the time. Making matters worse, because of changes in the way the numbers have been issued since 1988, the numbers are getting easier and easier to guess as time passes. But instead, their newly educated guesses have narrowed the odds down to roughly 1 in 1,000.

That's what the Carnegie Mellon researchers found.Ī completely random guess at a 9-digit SSN should be a one in one billion chance. Even a small discovery of such a cluster can make an enormous difference to someone trying to crack a crypto code, making predictions of supposedly random numbers an order of magnitude easier. With a large enough sample, the numbers begin to form clusters. Often, software programs designed to create random numbers erroneously spit them out with a faintly distinguishable pattern. Developing perfectly random numbers - the science of cryptography - is nearly impossible. But to mathematicians, randomness is a sliding scale. To most people, a number is either random or it's not. It involves the elusive concept of randomness. Acquisti said he's discovered simple patterns in the Social Security numbering system.

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