Police are baffled after they found a communication operation that was running with hundreds of mobile phones, tens of thousands of SIM cards and dozens of routers in Negombo.
Police say they recovered 17,400 SIM cards, 400 iPhones, two Android phones and 60 routers from the location in Ethukkal in Negombo.
All the phones were connected to the internet at the same time.
One of the men under detention is a Chinese national, who did not have a valid visa for Sri Lanka police said.
The raid was conducted by the STF after a tip-off that there was suspicious activity in the house.
The Criminal Investigations Department (CID), the Telecommunications Regulatory Commission (TRC) and Sri Lanka Telecom are at the location conducting investigations.