A computer virus that has been spreading around the world for months is set to come alive Wednesday.
Experts have struggled to tackle it, and they do not know who controls it or why it was created. But on Wednesday the virus, dubbed Conficker, will "call home" to its creator to seek new instructions. No one knows what will happen next.
"The biggest mystery about Conficker is why? What exactly is it that these bad guys are planning to do with it?" said Mikko Hypponen of the Finnish computer security company F-Secure.
In the past year, the virus has spread to computers in schools, hospitals and government departments. It has got into the defense forces of Britain, Germany and France, grounding the French Navy's fighter jets for a time.
Microsoft has offered $250,000 for information about Conficker's creator. An alliance of leading computer security experts and Internet governance groups has been set up to help to deal with the problem.