Just as a virus that affects humans can mutate and confound medical experts, each version of Sasser -- labeled A, B, C, and D -- poses slightly different challenges for information technology experts.

CNN: Sasser worm rips through Internet

The chronic version of the condition -- which is defined as lasting for 12 weeks or more -- affects about 1 in 6 adults in the U.S., according to the study.

CNN: Sinus trouble? Secondhand smoke may be to blame