Risk: Informational
Every so often a computer virus becomes more than just a novelty for anti-virus researchers and moves into the consciousness of the mass media, even if it's not a grave threat.
The recent Conficker outbreak is a fantastic example of this. While only a small fraction of all PC users were infected with the worm, a great deal of media coverage was devoted to the outbreak.
Concerned users ended up cleaning up their systems from a multitude of other malware, even if they have never encountered the Conficker worm itself, leaving the overall population of systems cleaner than they were previously.