An anonymous reader writes "Recent media reports indicate that in 2005-06, the FBI went trawling through grocery store records in order to track down Iranian terror cells. They hoped to be able to locate Iranians through the purchase of specific food items. The problem with this, of course, is that most Iranians buy their middle eastern food at small ethnic markets, and not the big supermarket chains — for the simple reason that muslims are required to eat halal meat, which is not sold in most places.
The majority of mom and pop ethnic markets do not have the detailed computer purchase histories that Safeway or Whole Foods have. Thus, what is more likely is that the FBI simply put together a list of everyone who had purchased anything at a middle eastern food market. As this "CNET article discusses, all signs point to the credit card companies (Visa, Mastercard, Amex) providing this data, and not the individual stores. This could be the tip of a (potentially illegal) data-mining iceberg.
http://www.cnet.com/8301-13739_1-9812473-46.html"Link to Original Source