BOSTON -- Some 500 senior citizens in Wellesley are now worried their identities may have been stolen after they got flu shots.

NewsCenter 5's Steve Lacy reported that the seniors got the flu shots last fall and then, last week, the town sent an envelope with all their personal information, including names, ages, addresses and Social Security numbers to Medicare as part of the reimbursement process.

The envelope arrived but was missing the list of names, according to the Boston Globe. Wellesley police were notified and launched an investigation, as has the U.S. Postal Inspection Service.

The sealed envelope was reportedly hand-delivered to the post office for mailing, which reduces the chances the information was stolen. It is possible a mechanical malfunction within the postal service is to blame.

Seniors whose information is missing should look out for signs of identity theft, officials said. One possible sign of ID theft is if consumers fail to receive bills, because thieves sometimes change mailing addresses to cover their tracks. Another is if consumers receive credit cards they did not apply for or if they are suddenly denied credit. Also, if consumers receive telephone calls about items they have not purchased.

The town said it will be mailing letters to anyone effected by early next week.