THE conventional way to protect intellectual property is to patent it. This gives an inventor legal protection for his idea: if others want to use it, they must pay him. The snag is that he must publish his idea, making it easy for someone in a less lawful country to steal it.

So a lot of companies are keeping their most valuable ideas under wraps. Alas, this is not foolproof, either. Hackers are cunning, and China employs thousands of them to steal foreign secrets, as a report last month from Mandiant, a computer-security firm, made clear.

No one knows how many trade secrets companies keep, or how much they are worth. Some, like customer lists, are generated during day-to-day operations. Others are kept secret because patents typically last only 20 years. Had Coca-Cola patented its secret recipe, it would have lost the rights to it long ago. And it would have lost its mystique straight away.