C ambodia's mobile telephone companies - already struggling to make a profit - are

under siege from high tech thieves who are hacking into networks in order to make

free overseas calls.

Company executives are unsure as to the exact scale of the fraud, but one said it

could run into hundreds of thousands of dollars.

The Post is aware of at least three recent cases where Phnom Penh subscribers had

been billed for a total of nearly $5,000 for calls they had not made. In each case

the phone company had absorbed the cost of the calls.

In one case, a foreign UN worker had been confronted by her supervisor with a bill

for more than $1,200 for overseas calls made over a three day period in late November.

However, the woman was overseas at the time the calls were made.

"I left Cambodia for a short holiday, leaving my phone hooked up to the battery

charger," she said. "When I returned the phone wouldn't work and then I

was confronted with the bill.

"Most of the calls were made to China, but there were others to Russia, France

and the Canary Islands," she said. "When we went to the company's office

to query the bill, there was a Cambodian businessman with the same problem. He had

been charged $800 for calls made to China and the US over a twelve hour period."

Though the problem is new to Cambodia, hacking into analog phone networks - or cloning

as it is known in the industry - is a well established international criminal practice.

A recent article in the New Scientist magazine put the cost of cloning to the British

cell phone industry at $300 million a year.

Cloning operations are usually associated with "cut price" services offering

international calls at very low prices - a common practice in popular tourist destinations

like Thailand. But they may also be set up by otherwise legitimate businesses seeking

to cut the costs of their international phone bills.

The operation is difficult to detect until a questionable account is presented and

the equipment required is both widely obtainable and cheap. The software programs

required to activate the scam is available free on the Internet.

Cell phones - the most common type of mobile phone - each have two numbers: the ordinary

phone number and a coded serial number which allows the phone system to recognize

a hand set as belonging to its network.

Both are stored in the circuitry of the phone - when it makes a call the matched

pair of numbers is "read" by the nearest base station enabling the system

to check that the phone is authorized to make calls.

Stolen phones, however, can be reprogrammed - or cloned - with numbers obtained by

a scanner tuned to the control channel used by mobile phones. Phones which are left

on but not used for extended periods are particularly susceptible as they continuously

communicate with the nearest base station through the control channel.

Once cloned, the original hand set will likely develop operating problems, but if

the legitimate owner is not using the phone, the cloning will go undetected.

According to New Scientist , until recently criminals could only obtain matched pairs

of numbers one at a time. Now they have a device that can steal the identity numbers

of all the cell phones within a one kilometer radius within a matter of minutes.

Because such a system allows criminals to constantly change stolen numbers, they

are even more difficult to apprehend. The only real weapon against cloners, according

to cell-phone companies quoted in New Scientist , is an international ban on scanning

equipment used to access phone networks.