The hope that 2006 might end without yet another breach of personal information was dashed when 170,000 Wisconsin taxpayers were notified that their tax forms were being mailed out with Social Security numbers visibly printed on the front.

Wisconsin's Department of Revenue stated that taxpayers who had filed returns in 2005 using the paper Form 1 were affected. Those who filed their forms with professional tax preparers, filed different forms, or e-filed were not in danger, the department said.

The mistake was blamed on a "computer error."

The tax agency said it would notify all potentially affected taxpayers, and also notified the postal service to locate and return as many of the forms as possible.

Department spokeswoman Meredith Helgerson said that they could not estimate how many of the labels made it through the mail.

Helgerson said the agency and the postal service would take advantage of the four-day holiday due to New Year's and the day of mourning for former President Gerald Ford -- with the resultant lack of mail delivery -- to find and collect all of the mislabeled forms.

Wisconsin's Revenue Department had mailed forms out with Social Security numbers visible on them for years, until the state legislature and former governor Tommy Thompson pressured the department to use special identifier numbers instead.

Thompson, also a former Secretary of Health and Human Services, ironically went on to become a chief advocate of the usage of radio frequency identifier (RFID) tags, or "spychips," in medical patients and soldiers.

Clear and Present Danger

The chief concern was that criminals would steal the forms from unopened mailboxes and use the Social Security numbers for identity theft.

Social Security number-based identity theft is particularly difficult to detect and prevent, as criminals can mix and match names and numbers to create new identities and open credit accounts without being noticed.

Credit reporting agencies simply open new credit files for accounts using the same number, and don't notify the original or new account holders. SSN-based fraud can go undetected for years until the original account holder receives bills belonging to the thief.

It's extremely difficult to change a Social Security number once it's assigned, and even if the accountholder gets a new one, the account is often linked to the old account to ensure the recipient receives their Social Security benefits.

The Wisconsin incident is not the first time in recent months a printing mixup has led to potential risk of identity theft.

In November 2006, a contractor working for the Chicago public school system accidentally sent out the personal data of 1,740 employees and retirees as part of a mass mailing of health insurance benefit plan information.