New Delhi, Jan. 9 -- Cambodia's arrest and extradition of a powerful tycoon accused of running a vast online scam network marks a rare strike against an industry that has stolen tens of billions of dollars worldwide. U.S. and U.K. authorities say Chen Zhi led a transnational criminal enterprise that exploited trafficked workers and defrauded victims worldwide.

For victims, the scams often start small: a text offering a part-time job, asking about weekend availability or simply saying "hello." On the other end is often a laborer halfway around the world, forced to work 12- to 16-hour days, sending message after message until someone responds.

That human toll is immense. Hundreds of thousands of people are believed to be trapped in forced...