There is no such thing as a wholly secure computer network. However sophisticated the software, however complex the security systems, there will always be a flaw. That does not mean the hackers will necessarily find it, but it will be there. And the chances are, especially in the biggest and most sensitive networks, that there will be a further weakness: the knowledgeable insider who may sell his information or give it to some plausible conman smart enough to ask the right questions. Hence the success, no matter how hard banks and other financial institutions work at their security, of the so-called cyber-terrorists. These extremely sophisticated criminals have managed to extort multi-million dollar ransoms from Western banks and broking houses. They know not only the weaknesses, but also how to hack in and leave coded 'logic bombs', a kind of super-virus which can destroy enough valuable data to bring a bank to its knees. At least four such cyber-gangs, working out of the United States and Russia, are known to police and intelligence agencies. So it is only a matter of time - if it has not already happened - before Asian banks are also threatened. Financial institutions are, by their nature, reluctant to expose their weaknesses - even to the police. For this reason, no one knows how big the problem really is. So what is to be done? While police forces across Europe are banding together to combat cyber-fraud, their cross-border co-operation in many fields remains, at best, rudimentary. Also, police commercial crime units are ill-equipped to deal with such sophisticated hackers, and may not get full co-operation from banks. What is needed is help from the people believed to be behind the development of logic bombs. The expertise is thought to come from the US military, which is developing them to disable or destroy enemy computers. If so, it is more important than ever that the intelligence and security services become involved in countering the threat against civilian installations. Security agencies not only in the West, but also in the former Soviet Union and Asia must overcome their mutual distrust and work together. Only then can international cyber-terrorism be stopped.