At the former eBay Enterprise/GSI Commerce headquarters in King of Prussia -- the company, under new private-equity owners, will be renamed soon -- Michael Graff's Fraud Technology Lab is measuring online ripoffs that drive online-sales losses higher. The idea isn't to scare off buyers, but to show merchants how to cut the risk of loss (and get them to hire the service.).

The busiest days for online fraudsters? New Year's, when digital gift-card fraud jumps to $6 for every $100 ordered, from the usual sub-1 percent; Christmas Eve, when overnight-delivery fraud jumps from the usual 1 in 100 packages to 1 in 20, "as criminals take advantage of procastinators" to steal boxes off porches; and any Wednesday, so deliveries can be timed for Fridays and stolen merchandise enjoyed "over the weekend," Graff says.

Graff has used eBay analytics to map fraud -- and finds it concentrated, not just in entry ports like New York, Seattle, Miami, the Texas border -- but also in the Portland, Ore. and Wilmington, Del. area. Both impose no retail sales taxes, and have attracted busy concentrations of "freight forwarders," warehouse-based middlemen who among their other clients attract criminals, who direct jewelry and electronics purchases through the fraudsters to their mail-drops, then skip on the bills.

In Oregon, Florida and Delaware, fraud eats more than 70 cents of every $100 spent online; in most states it's below 25 cents. Loss rates are much higher for compact, high-value goods: For jewelry sent online, the loss rate is $8.68 for every $100; for electronics, $7.35 per $100; shoes, $3.21 per $100. Sporting-goods and cosmetics are also above-average thief magnets.

Knowing all this -- have merchants and shippers started charging premium prices for higher-risk sectors and markets? "That's not part of the equation yet. But we are using very similar risk and fraud algorithms, as the ones the financial industry is using," says Tobias Hartmann, chief executive of eBay Enterprise, and Graff's boss. Financial companies, including insurers, do try to price risky customers higher: it's why smokers pay more for health insurance and young drivers for rental cars.

eBay Enterprise, which helps retailers run their online-delivery networks in competition with Amazon.com, only gets paid for successful transactions, so it has a strong incentive to find and stop fraud. Graff says his retailer clients are sometimes reluctant to ship across the country, or overseas, associating long deliveries with higher fraud risk. But his analytics show "that's not always the case": freight forwarders can "throw off the algorithms," handling legit long-distance sales and actually reducing fraud risk. His argument: retailers need sophisticated analysis to know where risk really is.

Freight-forwarders aren't obliged to disclose who their customers are. Law enforcement is divided by state and local jursidiction and often ineffective in stopping small-scale chronic frauds. That makes national consultants like eBay Enterprise more attractive to expansion-minded retailers.

Graff's group sometimes picks up less-sophisticated signs of fraud, and even murder. Last summer, "one of our analysts caught a very suspicious looking order," a purchase that didn't fit the buyer's previous retail pattern. The company reported it to the merchant, "and the next day we got a call from a Philadelphia homicide detective. Someone had stolen the payment information and used it to make a fraudulent payment. The police were able to find the person using information we supplied." The legitimate card owner was dead; the man who took the cards has been accused of the murder.  Here's the case.

Fraud never sleeps, Graff concludes. "Tere's an 'evil Michael' doing the opposite of what I do, finding the weak spots in fraud detection," he told me. "Business is booming, for him. He will continue to get better."