If you want to pay for sex in the United States — or offer sex services for a fee — and you’d rather not troll derelict city street corners late at night, chances are you’re going to use backpage.com.

Of course, Backpage’s adult classifieds are cloaked in the coy poetry of online sex advertising; you’re searching for an “escort” instead of a “prostitute” or a “full body sensual mutual touch” instead of something more crudely sexual. But recent studies from the Advanced Interactive Media Group (AIMG) cut through coyness to offer at least one blunt statistic: About 70 percent of the revenue generated from online sex transactions in the U.S. goes to Backpage. Last year, AIMG figured Backpage generated around $2 million in revenue every month from online sex sales.

To put it another way: The Village Voice Media-owned online classified ad service could be seen as the main source for online sex in the U.S.

And with Craigslist no longer offering sex services on any of its 700 sites around the world (Craigslist dropped its “adult classifieds” section in 2010), Backpage’s adult market share has nowhere to go but up.

But there’s a hitch. And that hitch not only threatens to put Backpage out of business. It also threatens to completely change the way websites handle third-party content.