If you eat Doritos for dinner every night, here are two pieces of advice: First, rethink your dietary choices. And second, don’t be surprised if at some point in the future you begin to see more TV commercials that reflect your appetite for salty snacks.

Television, long perceived as a passive medium, is getting smarter about delivering ads based on your likes and behaviors, thanks in part to new audience-targeting tools being rolled out by media companies. But just as targeted ads on the Internet have done for decades, these new capabilities are raising red flags among privacy advocates who worry about the implications of television programmers combining large sets of consumer data with information about viewing habits.    

“TV has lost the quality of being a one-way thing where you watch it but it doesn’t watch you,” said Lee Tien, a senior staff attorney for the Electronic Frontier Foundation in San Francisco.  

TV’s coming era of ad targeting was underscored on Thursday at an “upfront” presentation in New York, where NBCUniversal announced it will gain access to viewer data from set-top boxes owned by Comcast Corp., its parent company and the largest cable operator in the country.

The change, which will take place at some point during the 2015-2016 broadcast season, promises to supercharge NBCUniversal’s newly announced “audience targeting platform,” or ATP, which combines viewer data from set-top boxes with third-party data about consumers’ behavior, purchase history and interests. Together these sources of information are a powerful indicator of what viewers like and dislike: Over the years, data brokers and retailers have amassed vast troves of information about our most intimate habits, while cable equipment has become more advanced at generating activity data about what shows people watch, when they watch them, and even how many people actually sit through the commercials.

Programmers say these data sources together can give advertisers laser-focused insights that go way beyond the typical demographic information from Nielsen TV ratings. “Marketers no longer have to choose between digital media’s data-driven targeting and television’s scale and unparalleled ability to communicate via great storytelling,” Linda Yaccarino, NBCUniversal’s chair of advertising sales and client partnerships, said of ATP when it was announced in January.     

NBCUniversal owns a number of popular cable channels, including USA and Bravo, in addition to the NBC broadcast network. It is not alone among big media companies in pushing new data-driven ad initiatives during this year’s upfront season. Turner Broadcasting, owner of such networks as TBS, CNN and Adult Swim, recently joined the targeted-advertising fray with a product called “Audience Now.”  

NBC Pedestrians walk past the entrance to the NBC studios, outside Rockefeller Center in New York. Photo: Reuters

TV Needs A Savior

Such tools obviously hold great promise for programmers as traditional TV ratings decline and advertising dollars shift from television to digital. If networks hope to stop the bleeding, they’ll need to get to know their audiences more intimately: Are reruns of “The Big Bang Theory” popular with frequent Starbucks customers? Do people who purchase NyQuil prefer to nod off to Jimmy Fallon or Jimmy Kimmel? Matching consumer purchases with viewer data from set-top boxes is a great way to find out.

But legal experts say Comcast and other cable providers will have to tread carefully lest they run afoul of long-standing privacy laws designed to protect pay-TV subscribers. The Cable Communications Policy Act, passed more than three decades ago, places serious restrictions on cable operators in regard to how they may use the data that is collected and stored by their equipment.  

“People realized pretty early on that, if you have a cable box, you can figure out what people are watching at any given time, and clearly you don’t want your cable TV provider to be tracking every last bit of your viewing habits without you knowing it,” said Sherwin Siy, vice president of legal affairs for Public Knowledge, a Washington-based public-interest group that focuses on communications and technology.

A Comcast spokesman said protecting subscriber data is a top priority and stressed that the information from its set-top boxes will never leave its control. He said Comcast is not sharing personally identifiable information about its customers, but simply providing a software tool that allows programmers, like NBCUniversal, to run certain queries. (The tool may also be made available to other media companies if agreements can be reached.) Those queries, in turn, will produce aggregated, anonymized reports that will help TV networks identify top-performing inventory among specified audiences.

That’s all well and good, Tien said, but as with any initiative that involves customer information, the devil is often in the details, and not everyone agrees on where companies should draw the line. “I would ask them, How are you technically implementing that?” he said. “Exactly what data is generated in the process, and then how do you process that data in a way that it does not or cannot reveal the things that you say that you’re not trying to reveal?”

He added that it’s very easy to “de-anonymize” a customer if you have enough data about them. Further clouding the situation is that the standards of data collection and sharing are often legally ambiguous. “Different people will mean different things when they say ‘anonymous,’ ” Siy added.

The ‘Creep’ Factor

Internet users have long accepted that their browsing history will follow them around. Even if it’s creepy to see ads for that Ben Sherman sweater you glanced at pop up on 20 different websites, it’s something we’ve gotten used to. Ad targeting on television, however, will look much different. Current tools aren’t designed to deliver individualized commercials to each viewer, but rather to give advertisers deeper insight into what types of consumers are watching which programs.

In other words, you and your next-door neighbor won’t see different commercials just because you have different interests, at least not yet. But media companies will be digging into those interests in ever more intricate ways, and it’s anyone’s guess as to how deep the information will go. NBCUniversal declined to say which third-party entities it was working with to obtain consumer behavioral data.

Privacy advocates say a big part of the concern lies with data brokers -- loosely defined as companies that collect and sell information about consumers -- which are vastly underregulated compared to other industries. In fact, many consumers are still unaware that data brokers even exist, and it’s only in the last few years that policymakers and government regulators have begun to pay attention to them.

In the meantime, just assume that almost every purchase you make is fair game. Consider that loyalty card you swipe when you shop at Walgreens, whose shelves are lined with items that are indicators of various different health conditions. The Health Insurance Portability and Accountability Act, or HIPAA, protects patient confidentiality within the healthcare industry, but entities that collect everyday consumer shopping data fall outside of its reach. “The actual pharmacy is covered by HIPAA,” Tien said. “But if you’re buying aspirin at Safeway? No, that’s quite different.”

The distance between that bottle of aspirin and your secret love for the “Real Housewives” franchise is getting shorter. Combine that with your travel habits, book purchases, personal hygiene products and any number of retail breadcrumbs you leave behind, and it’s easy to start feeling a little dizzy when you sit down to watch that once-passive box.

Christopher Zara is a senior writer who covers media and culture. News tips? Email me here. Follow me on Twitter @christopherzara.