Lack of agreement about what constitutes a different computer virus. Family boundaries are ill-defined. We are content to let people enjoy their debate. Eventually, some good may come of it. Software tools which monitor user behavior in certain limited environments might be very useful supplements to such a survey.
Some additional remarks apply to all of the questions posed in the previous section.
Whether the information is obtained via surveys or by closely monitoring a large population of users, care must be taken in gathering and interpreting the data. We must define the quantities we are trying to measure carefully and make sure that the data we gather actually measure those quantities and that they are accurate. Even if the data are accurate, there are many pitfalls that must be avoided in their interpretation. For example, both the Certus and Dataquest studies have blurred the distinction between the number of incidents and the number of infected machines, and have in some cases failed to distinguish between the number of infections by one particular virus and the number of infections due to all known viruses. As we will see, attempting to extrapolate from noisy or incomplete data is another such pitfall.