Marko said he offered the domain to XNXX due to its reputation for professionalism and strong adult traffic.
"After three years of work, I decided to sell," he told AVN Online. "I decided it was better to sell the domain to a company that had the time and resources to monetize its traffic. I'm sure their partners will benefit largely from the purchase."
LemarkXNXX will act as Adult Biz Forum's new administrator, and the forum's previous administrators plan to stay on board as regular members.
"Lemark is an incredible guy," Marko said. "I'm very confident he will bring the forum to a new level as its new administrator."
Plans for the site include small changes during the transition and new features in the future.
Marko said selling Adult Biz Forum will allow him to focus on his company Adult Biz Production, which offers hosting and content production.
"I plan to offer many more services to firms and webmasters in the future, now that I have the opportunity to concentrate on things," he said, adding that Adult Biz Production will employ more quality freelancers.