Earlier quoted context omitted.
Probably the same math they use to calculate our credit scores and everything else they screw up.
The math behind credit scores is quite good. They're very effective at predicting credit risk.
I hope I have bought enough street cred to say the following by ghostwriting hundreds of letters to the credit reporting agencies to fix their problems, which are numerous and essentially inevitable given their model and present operations.
Credit scores are important because they allow banks to do standardized, automated underwriting for effectively free at 2 AM in the morning, which is what makes credit abundantly available in the United States and one of the reasons why it is so cheap to the middle class. (This routinely escapes the notice of people in the middle class, but the ordinary operation of banks is to advance well-organized people money for free and pay you to be chosen to do so, partly due to credit scores making this a derisked proposition and partly due to interchange revenue.)
Credit scores decimated the costs of unsecured consumer loans, as is readily observable by seeing what loan availability, pricing, and the "credit box" looks like when they're not available for underwriting. (This is a term of art in consumer credit that I provide for your future Googling pleasure, not having enough time to explain it at the moment.) Compare the cost on a cash advance on any card in your wallet to a payday lender. That delta is substantially (not solely) due to credit scores, both in improved understanding of default risk and in reduced operational cost (of underwriting and servicing, both enabled by the scoring infrastructure).
Credit scores are an important justice-enhancing technology because they make the inputs to an underwriting decision objectively observable and for the first time in history those inputs provably do not include race, religion, etc.
There is an argument which is not immediately dismissible that credit scores are based on borrower behavior which reflects the socioeconomic realities of the United States and therefore somehow effectively encode race, but it is an obvious improvement that banks now mechanically reach the same decision on similarly situated white and black borrowers. Regulation did not make that happen. FICO did.
I think well-off computer programmers should understand that there is a societal tradeoff which buys "middle class black Americans have the same access to credit you do" at the cost of Equifax knowing your credit limits; understand that if you are advocating for rolling back the second you should accept that ceteris paribus we will experience material disimprovement on the first.
(Obligatory disclaimer: personal opinion here.)