As it turns out, snooping federal agencies probably have nothing on private data collectors and aggregators. Their focus isn’t national security; it’s creating a profile of your likes, dislikes and behaviors to figure out ways to sell you stuff.

With fresh disclosures about the extent of the National Security Administration’s surveillance of America’s telephone and Internet communication habits coming practically on a weekly basis, you’re probably not the only one looking over your shoulder (figuratively, at least) and wondering what kind of digital dossier the government is keeping on you.

As it turns out, federal agencies probably have nothing on private data collectors and aggregators. Their focus isn’t national security; it’s creating a profile of your likes, dislikes and behaviors to figure out ways to sell you stuff.

“The key problem with commercial use of data is when somebody has a ton of data on you, they can essentially trick you into a transaction that’s not in your best interest.,” says Holmes Wilson, co-founder of privacy advocacy group Fight for the Future. Having a wealth of information about how you shop for and buy stuff, what you like and dislike all helps marketers plan subtle suggestions you’re liable to respond to because you don’t even realize they’re there.

And it’s not just your online behavior being monitored. The New York Times recently wrote about high-end department store Nordstrom having to scrap a pilot program to track shoppers in stores after people complained.

The article explains what and how one such company “can pinpoint where the shopper is in the store, within a 10-foot radius, even if the shopper does not connect to the network… The store can also recognize returning shoppers, because mobile devices send unique identification codes when they search for networks.”

This sounds creepy, but avoiding all this tracking is harder than you think.

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“The unfortunate thing is that whenever you do anything that touches electronic media you’re potentially creating data that could be used in different ways without your knowledge or consent,” Wilson says. And even if you’re in a store, that phone in your pocket is probably whispering your whereabouts to a server somewhere.

Here are the main reasons you’re on Big Data’s radar.

1) You can’t stay off social media. Companies of all kinds are figuring out ways to profit from the status updates, likes, and other information we willingly volunteer on social media sites. Wilson says sites like Facebook collect information about what users are doing for two reasons: To figure out ways to get them to stay on the site longer, and to help its advertisers do a better job targeting display ads and those “sponsored stories” that show up in your news feed. ’”Its probably safe to say they’re looking at everything,” Wilson says. “It’s getting more granular all the time.” Social networks look at who and what you’re connected to, and when and where you communicate.

2) Your web browser is an open book. Aleecia M. McDonald, a privacy researcher and resident fellow at the Stanford Center for Internet and Society says web ads invisibly assign a unique number to each computer to make a digital profile of you, noting your interests, what sites you visit, the news you read and the things you buy online. “All of this happens invisibly,” she says.

There are steps you can take to limit this data-gathering, but McDonald says most people don’t bother. You can bump up your privacy settings in your web browser, blocking access to your location or cookies from sites you haven’t visited. “All of these are easy things that take under five minutes to do with the Preferences settings built into all web browsers,” she says.

3) You’re hooked on coupons. While most people can’t be bothered to change their online habits even if they have some sense that their data is being logged, many others “see the upsides of being tracked—they get better deals and tailored offers,” says Sheri Roder, chief of The WHY Group, a division of media agency Horizon Media.

Robert Plant, associate professor of computer information systems at the University of Miami School of Business Administration, says the oldest — and one of the most successful — data-mining initiatives is the loyalty program of British supermarket chain Tesco, which has been keeping track of who buys what and sending them offers since 1992. A lot of people like the idea of getting discounts on the items they buy most frequently, and this kind of data-gathering is generally anonymized and aggregated.

(MORE: Future of Retail: How Companies Can Employ Big Data to Create a Better Shopping Experience)

4) You let your phone spy on you. All of the online tracking of your browsing habits also takes place if you’re using your phone to surf the web, shop online, or comparison-shop for prices when you’re in a store. But our mobile devices are more valuable to data gatherers than your desktop computer because your phone also shows companies where you are.

“When you have your cell phone on, if you have either your wi-fi on or your bluetooth, your phone is broadcasting a unique number,” says Jules Polonetsky, director and co-chairman of the Future of Privacy Forum. “They’re basically treating it as a cookie.” Stores and shopping centers can use this information to see where you’re going, what stores you visit, what parts of the store you go to, and where you linger. To keep those electronic eyes off you, you have to remember to turn off your phone’s wi-fi and Bluetooth before each shopping trip.

(MORE: When a Retailer Asks, ‘Can I Have Your ZIP Code?’ Just Say No)

5) You’re a sucker for free apps. “Before you download a mobile app, read the agreement associated with it. Some want to track your location as well as wanting access to other information about you,” Roder says. Especially free apps, like those time-killing games everyone’s addicted to, need to make money somehow, points out Plant, and data can be turned into dollars relatively easily.

“The app could be anything. It could be a horoscope or something, but you don’t know what it’s really doing in the background,” Plant says. In a study of more than 100 popular apps, the Wall Street Journal found that most collect information like the user’s location and the unique number every phone is assigned (think of it as your phone’s Social Security number).