They are armed with guns, clubs, and knives. They stalk their "prey" in fishing boats. The victims of these modern-day pirates are desperate Vietnamese refugees who risk their lives in a quest for sanctuary. Their elusive goal is the beaches of southern Thailand and Malaysia.
But increasingly they find themselves prisoners of brutal captors who steal their gold, rape the women, and beat or knife the men to death.
It is a problem that has gained growing attention. Efforts to combat the abuses are also growing. But so far refugee experts here say far too little is being done to meet the problem.
This month the United Nations made a high-speed patrol boat available to the Thais to enable them to respond quickly to any reports of refugees being menaced by pirates. Based in the southern Thai port of Songkhla, the 26-ton vessel manned by a Thai crew will be on instant call to help rescue pirate victims taken to the Thai coastal island of Koh Kora where thay are often "freed" to be hunted down, beaten, and killed or raped.
Previously only three Thai Navy patrol boats cruised the Gulf of Siam. The boats, frequently experiencing maintenance problems, were inadequate to patrol an area stretching from Bangkok to Malaysia.
But experts here regard the UN vessel as representing only an exceptionally modest solution.
Some 12,000 to 20,000 Thai fishing vessels cruise the Gulf of Siam. Many of these are honest fishermen. But some occasionally turn to piracy either out of sheer greed or because of declining living standards caused by rising diesel fuel prices and increasingly fishd-out seas.
Face to face with a vessel loaded with helpless refugees, there may be an overwhelming temptation for the Thais to steal. Some Thais strongly dislike Vietnamese. And all-men fishing crews sometimes see Vietnamese women as targets for abuse.
So, even with the aid of the UN vessel, the underequipped Thai Navy faces a formidable task in determining just which vessels are manned by honest fishermen and which are manned by pirates.
Also there is a growing ring of professional full-time pirates, possibly linked to syndicates in Bangkok, according to some sources. These run in packs capable of scouting out weak, unarmed refugee vessels and then pouncing.
Many devoutly Buddhist Thais abhor the brutality of the pirates. But the Thai Navy is more heavily concerned with patrolling the waters near Vietnamese-occupied Cambodia.
The three Thai patrol boats stationed in Songkhla have had little effect. One reason frequently given is maintenance problems, which the United States has tried to help remedly with technical aid.
Others suggest that gangster elements in the Songkhla region are so strong that any police or naval officer who vigorously tracked down pirates might be shot in the back.
Another school of thought believes the Thai government is not that eager to clean up the piracy problem because the presence of pirates may deter an even greater number of Vietnamese refugees from landing on Thai shores.
Some Thai officials are reported less concerned over the anti-Vietnamese piracy because they believe refugee ships contain communist agents sent to join communist-leaning Vietnamese already living in Thailand.
Still the pirates, who are both Malay and Thai, do not prey on Vietnamese alone. Thai fishermen are frequently targets.
So far a significant effort has been made by the US. Four-engine P-3 Orion anti-submarine planes frequently overfly the Gulf of Siam. If they spot trouble , they pass on an alert. US Navy ships have picked up nearly 700 refugees in the area.
But the gradual movement of the American Navy to the Indian Ocean to deal with the Iran and Afghanistan problems has meant a declined presence in the Gulf of Siam.
This gives the pirates a freer hand.