If you borrowed to buy your home, chances are TheNumber knows a good deal about you.

The New York-based startup sucks-in data from marketing firms, public loan filings, courthouses and dozens of other sources, and sells it to mortgage bond and loan traders.

The vivid detail the company turns up—the types of stores borrowers tend to shop at and whether they rent out their homes on Airbnb Inc., for example—may unsettle privacy advocates, but it’s a boon for investors trying to figure out how likely homeowners are to pay their obligations.

“We can do things that were not possible before,” said Hans Thomas, a serial entrepreneur who co-founded the firm in 2015 with Guhan Kandasamy and Ziggy Jonsson.

The information the company compiles could have previously taken weeks or even months to track down, and now it takes seconds.

Across the world of finance, startups are using big data to try to improve Wall Street’s success with everything from consumer lending to stock trading.

Privacy Concerns

Good data is critical for investors in the $9 trillion mortgage bond market. For subprime securities, prices can widely vary due to the differing quality of loans backing them, and being able to compare bonds quickly can be the difference between finding a bargain and getting stuck with a turkey.

The average fund manager can gain 0.40 to 0.70 percentage points of return by using more intelligent data when trading mortgages, at least for home loans that have not been bundled into securities, according to John Ardy, chief executive officer of Resitrader, an institutional marketplace for home loans.

But giving so much mortgage information to investors so quickly is raising fresh concerns among consumer-rights watchdogs that borrowers could suffer a loss of privacy, or even discrimination.

“We’re concerned about how this information is shared, and how it can have adverse consequences for individuals without their even realizing it,” said Lee Tien, a senior staff attorney at the Electronic Frontier Foundation, a non-profit focusing on civil liberties in the digital realm.

Consumers may not understand how much of their information bond investors have access to. And money managers using information they get from TheNumber could face accusations of discriminating against borrowers based on race or religion, said Frank Pasquale, a professor at the University of Maryland’s Francis King Carey School of Law.

The Consumer Financial Protection Bureau in February asked for comments about the benefits, and risks, of using alternative data.

Kandasamy and Thomas say the company anonymizes some data, and can ensure that different professionals in an investment firm only see information they are legally allowed to see. It requires clients to agree not to abuse data, and it doesn’t give borrower names to mortgage securities traders.