IT IS HARD to think of a good word for something that has the potential to ruin the lives of millions of people as it multiplies and spreads around the planet. Fortunately we already have a good word: it is “virus”.“Virus” is good, because it has a shared meaning. There is no need to define our terms before we discuss it to death. In medicine, a “virus” is a parcel of genetic material that invades our cells, starts to multiply, and then either gives us a bit of a sniffle or kills us. On the one hand, it might be “justavirus”, the last resort of the hard-pressed GP: on the other, ebola.We had better hope that the scientific work to tackle ebola does not succumb to that other planetary plague, known as computer malware. The most famous type is