Many stores routinely ask for your zip code when you buy something, but what happens with that info?

Flickr User Pacdog

One expert warns it may go where you don't want it to go.

Paul Stephens of the Privacy Rights Clearinghouse says that the zip code, coupled with data from your credit card purchase, can be used to wring out personal info, including your address and phone number.

"Question, why am I being asked for this information? Is it essential to complete the transaction. And if it's not, then don't give up that information because it may be used in ways that you cannot anticipate."

As in junk phone calls and mail.

The National Retail Federation says in a statement, "Asking for generic information helps retailers tailor merchandise, customize advertising and marketing, promotions, deals and coupons and individualizes services."