Perhaps because of the big potential payoff and veil of anonymity, singletons online seem eager to overshare. eHarmony says it asks users as many as 147 questions, to increase the client’s chances of meeting someone with a compatible world view and personality. Last year, OkCupid co-founder Christian Rudder admitted that the site has analyzed user data. “Guess what everybody: if you use the Internet, you’re the subject of hundreds of experiments at any given time, on every site. That’s how websites work,” he wrote in a blog post. Of course, the more people learn about each other before that fateful first date, the better, author Slater says. “But nothing is free,” he says, “you’re giving them a ton of data.”

For their part, the sites say they don’t sell data to third parties. Instead, they use the data to improve matches, and to attract more users. “We realize the value of our database,” says Noel Biderman, CEO of Ashley Madison, a site with more than 15.5 million U.S. members that’s geared toward prospective extramarital affairs. (Biderman spoke to MarketWatch before the hack of the site.) The site’s database is a rich source for surveys, which are picked up by websites, magazines and newspapers, producing free publicity for the site. One recent survey, for instance, revealed that IT and engineering workers accounted for 11% of members and, as such, were judged to be the most likely to cheat on their spouses. The financial industry ranked No. 2., with over 8%.

While most sites don’t promote infidelity, some make it easy. Sites like DiscreetAdventures, MarriedSecrets and AshleyMadison cater to married men and women. Biderman founded the latter in 2001.

K.-based relationship advice charity, found that 38% of people say financial worries had led to more arguments and stress in their relationship

Facebook enables users to list their relationship status as senior match online single, and “friend” high school sweethearts and scroll through other people’s “friends” lists. A study published in the issue of the journal “Computers in Human Behavior” says increased use of Facebook is “positively correlated” with rising divorce rates during the same time period even when adjusting for economic and socio-demographic factors that might affect divorce rates. “Although it may seem surprising that a Facebook profile, a relatively small factor compared with other drivers of human behavior, could have a significant statistical relationship with divorce rates and marital satisfaction, it nonetheless seems to be the case,” the study concluded. A spokesman for Facebook says it’s “ludicrous” to suggest that Facebook leads to divorce.

Why the uptick in online affairs? Biderman – who says he is a happily married and also operates other sites, including CougarLife, for older women dating younger men, and EstablishedMen, “in the sugar daddy space” – says Ashley Madison took off in 2007, just before the U.S. financial crisis. It now claims 37 million members in 45 countries. “Challenging economic times lead to more marital discord,” he says. This theory appears to be supported by recent research. A survey by Relate, a U.

And OkCupid offers up to 4,000 questions at any given time, addressing an array of topics, from sexual proclivities to philosophy

Biderman says he merely facilitates infidelity and doesn’t encourage it. While sites like his may put temptation in people’s path, some experts say, the marriage and divorce rate has been unaffected by the Internet. “It does make it easier to cheat,” Reuben says, “but online dating makes it easier to fall in love and get married.” In fact, when people use these sites to cheat, they often leave an online trail, he says, “so it may even make it easier for people to get caught.”