Retail stores might know more about you than you realize. When you shop at stores today, you might unknowingly share information that allows the company to learn more about you than even your own family. This happened to a father in Minneapolis who discovered, from Target of all places, that his teenage daughter was pregnant.

After shopping at Target, the girl started getting mail at her dad’s house promoting baby products: diapers, clothes, cribs, and other items for babies. Her dad was furious about the company’s efforts to “promote” pregnancy in teens and complained to the management. A few days later, a embarrassed dad called the manager to apologize; it turned out his daughter was actually pregnant.

This is not an unusual occurrence with today’s computer-assisted data collections on the part of retail stores. Target assigns customers a Guest ID number that is tied to their name, credit card, email address and every other piece of information the store can collect. Using the information on past purchases, Target is able to create a startlingly accurate profile to use in customer-specific advertising.

In the case of the lucrative baby industry, Target looks at 25 items purchased by shoppers in various sizes to assign a “pregnancy prediction” score. The giant retailer notes that women in their first trimester tend to purchase calcium, magnesium or zinc supplements as well as unscented lotions. From that small piece of information, Target can then look at other purchases to make other predictions about a woman’s pregnancy like her current trimester and even her due date.

However, Target also realizes that sending baby ads to expectant mothers who have not announced their pregnancies can be intrusive. They often mix in random ads for other products to make the pregnancy ads less noticeable. This practice has helped Target earn over $67 billion in retail sales in 2010 at a time when many stores were going bankrupt, proving that other businesses could benefit from this type of data collection.