The notes issued by the Hong Kong Bank and Standard Chartered Bank bear a variety of security features that make the bills difficult to imitate. The Bank of China notes are no exception.

But, given the past form and entrepreneurial spirit of counterfeiters in Hong Kong, it may only be a matter of time before the new BOC notes are forged and distributed in the territory.

US dollars are the counterfeiters' most favourite choice because of the relative ease with which they can be copied. Besides, the currency is also readily accepted in Hong Kong and elsewhere in the world.

Identifying fake notes in Hong Kong and tracking down their source falls largely on the shoulders of Detective Chief Inspector Michael Yu Shi-cheung of the Commercial Crime Bureau.

Chief Inspector Yu, one of the region's foremost experts on counterfeiting, was consulted by the Bank of China on security features of its new notes.

He said that he advised the bank's experts to adopt security measures virtually identical to those of the two other Hong Kong note issuers.

But Chief Inspector Yu, who has trained abroad, has no illusions about the creativity of forgers.

''Let me put it this way: there is nothing in the world that cannot be counterfeited, but we must constantly review existing security features and introduce new ones to make it more difficult for counterfeiters to do their trade,'' he said.

''We have a duty to protect Hong Kong citizens and visitors from financial losses caused by counterfeit money.'' Chief Inspector Yu said the notes' security features should keep changing all the time for issuers to be always a step ahead of counterfeiters.

''I am confident that the security features in the new Bank of China notes will be every bit as good as those issued by the Hong Kong Bank and the Standard Chartered Bank,'' he said.

Over the past 18 months, fake US dollars with a face value of more than HK$60 million were seized in Hong Kong by the Commercial Crime Bureau, the Independent Commission Against Corruption and the US Secret Service.

Millions of dollars worth of equipment has also been confiscated and more than a dozen people have been charged.

A genuine Hong Kong note is printed by intaglio process that leaves an embossed effect on the surface, particularly over the bank's crest.

The appearance of counterfeit notes is usually quite rough because they are mostly printed by offset lithographic process or produced by colour copier.

The genuine note's paper is made of 100 per cent cotton, so it does not fluoresce under ultra-violet light. It is printed fluorescent ink.

The counterfeit note uses ordinary paper which normally fluoresces strongly under ultra-violet light.

A lion's head watermark image can be seen on either side of a genuine note if viewed against the light. A straight metal thread is also embedded in the note.

The simulated watermark and security thread in a counterfeit note are not clearly visible under ultra-violet light.

The genuine watermark is incorporated in the paper manufacturing process. It would be visible under ultra-violet light.

In fakes, the simulated watermark is printed on to the paper, making it invisible under ultra-violet light.

Some counterfeit notes are printed on two sheets of paper, with the simulated watermark printed on the inner side before they are stuck together.

This means the simulated watermark would not show up under the ultra-violet light unless the paper layers were stripped apart.

Another tell-tale sign of a genuine note are the fine lines, which are clear, sharp and continuous. The fine lines on counterfeit notes are blurred.

And the serial number of a genuine note should always be clear, sharp and well aligned. In a counterfeit note, the serial number is frequently blurred or printed in by a combination of colours.

Chief Inspector Yu, who commands a counterfeit and forgery section at the CCB, said he took comfort in the fact that Hong Kong notes were better protected by security features than many other currencies, especially the US dollar.