THE adult-entertainment industry recently posted a video on YouTube in which the actresses kept their clothes on, for a change. In a clip released by the Free Speech Coalition (FSC), a trade association, they begged viewers to pay for the porn they watch online.

These are tough times for peddlers of e-sex. Craigslist, a huge online marketplace, closed the “adult services” area of its website last week, under pressure from the attorney-general of Connecticut, a crusader against prostitution. That will mildly inconvenience internet pimps, but they will soon move to new websites. Pornographers are in bigger trouble, thanks to technology. The web has spawned so-called “tube” sites, such as PornHub.com, that post short clips from users. These are typically pirated and free. That somewhat undermines the porn industry's business model.

Under the law, the onus is on those who claim their content has been stolen to serve “takedown” notices. So porn studios face fat legal costs even as their revenues are falling. Gill Sperlein, a lawyer who works with the FSC, reckons some studios have seen sales drop by 30-40% in the past two years. For an industry that once thought itself recession-proof, that is shocking.

Since April, a group of studios has been using “digital fingerprinting” technology to make it easier for tube sites to spot pirated content. The aim is to get operators to block offending clips and replace them with legal ones linked to additional content that can be purchased. The tubes will then get a cut of the revenue generated.

But Peter Acworth of Kink.com, an online outfit that specialises in bondage, reckons that the best way to beat the tubes is to innovate more. His firm is experimenting with technology that lets viewers interact with performers in real time. And it plans to launch a social network, which will no doubt bind its members together very tightly.