The questionnaire came in a thick packet in the mail. The woman said she filled it out until its questions struck her as nosy and intrusive and her husband warned her it might be a scam.

“It made me uncomfortable,” she said. “I was going to throw it away or make up answers, but it says I’m required by law to fill it out. Is that true?”

I told her it is true. But while her husband was wrong, and the form isn’t a scam, she was right about one thing: It’s nosy. The line between Uncle Sam and Big Brother gets blurrier all the time.

The questionnaire came from the U.S. Census Bureau. It’s the American Community Survey, or ACS.

The Census Bureau started using it last year, sending it to 3 million households. It’s a sort of annual rolling census, going out to roughly one in 40 households, replacing the “long form” sent to about one in six addresses in the 2000 Census.

According to the Census Bureau, “Results from this survey are used to decide where new schools, hospitals and fire stations are needed. This information also helps communities plan for the kinds of emergency situations that might affect you and your neighbors, such as floods and other natural disasters.”

I’m sure it’s a gold mine for social scientists and community planners. But the devil is in the details, and the survey wants a lot of details – nine pages for an individual, 12 pages for a couple. The Census Bureau estimates it will take 38 minutes for the average household, “including the time for reviewing the instructions and answers,” but it could take almost that long to read the accompanying guide.

It asks about marital status, education, race, ancestry and physical and mental health. It asks about house size, lot size, house value, ownership, taxes, facilities and various utility costs. It asks where you work, what you do, what time you leave for work and how long it takes to get there.

And it asks about your income – not the range it falls within but the highly specific information you give the Internal Revenue Service.

The IRS is required to keep such information confidential. The Census Bureau isn’t allowed access, which makes the questions on its ACS look like an end-run on laws limiting disclosure.

Maybe it’s none of their business. When taking a census more than every 10 years was questioned in 2002, the U.S. comptroller general told Congress the Census Bureau had authority to conduct the ACS, but “we cannot state as a matter of law whether the requisite statutory authority supports each question.”

Did I mention the survey is not anonymous? It requires name, date of birth and phone number. It’s more than a head count.

Federal law says confidentiality is guaranteed, and violating the law carries a maximum penalty of five years in prison and a $250,000 fine. That would be more reassuring if personal data of more than 28 million people hadn’t been threatened by computer theft and Web glitches at the Veterans Administration, Transportation Department and Education Department in the past three months. The IRS, Social Security Administration, Department of Energy and Department of Agriculture also have had security breaches this year.

But the ACS brochure says your response is required by law. It took more research to find the penalties: a fine of up to $100 for refusing to participate and up to $500 for giving false information.

For the woman uncomfortable with nosy questions, I said it came to this: It’s like taking the SAT in high school, where you’re better off leaving a question blank than guessing wrong.

She wondered how they’d know if she made up answers – given the rules about privacy.

Good question. I had to leave it blank.