Google's data gathering has come under fire again, this time because of an art contest for children.

The Doodle-4-Google contest invites children to redesign the home page logo. The contest has been in place for four years, and this year the theme is What I'd like to do someday...

The problem was in the registration form, which asked for the last four digits of the child's social security number and the city of their birth, as well as the name and address of the parent or legal guardian.

Stories appeared in New York Magazine and The Huffington Post, but Google changed the registration form to omit the question about the last four digits of the social security number on Feb. 18, before the stories appeared. The Huffington post piece, authored by Bob Bowdon, noted that the last four digits of a social security number coupled with a birth city can make it easy to derive the rest of the Social Security number from there. Bowdon said that while he didn't have any evidence that Google was storing the data, such data would be valuable to advertisers.

In fact, the first three digits are based on where the Social Security number is issued, and the area lists are public. The second two digits are a group number which is issued in a regular (though not numerical) sequence. The last four digits are the serial number for the individual. If someone has the last four digits of a social security number, and knows that the person was born in a certain city, reconstructing the rest is comparatively easy.

For example, a serial number of 1234, coupled with a location - Madison, Wis., for example, and a birth year would mean that the person's social security number is likely to have the first three digits be 387-399. Knowing the date of birth and looking at the publicly-available High Group History List which shows which two- and three-digit numbers are being allocated when would enable someone to make a good guess at a Social Security number, even without a computer.

Narrowing the field further is the fact that no Social Security number can have a first three digits above 772, because when the area system was set up that was the highest number the Social Security Administration got to.

Google said it was using the SSN and birth city data to help eliminate duplicate contest entries, as well as test for eligibility. A spokesperson said the reason for asking for the birth city was to discourage applications from people who might not be the actual parent of the child and to flag entries that might require verification later. Meanwhile, the spokesperson added that the SSN data was not entered electronically because the entry forms were on paper. The data, he said, will be discarded.

To contact the reporter responsible for this story call (646) 461 6917 or email