For three weeks Voyager has been plagued by a computer virus, or "Trojan horse", picked up in a sector of the Delta Quadrant dominated by businesses. The virus allows "spam" advertising messages to penetrate the ship's systems, first interfering with communications and Janeway's log, then appearing on the bridge viewscreen, and even being delivered by the Doctor. Janeway sets Kim and Tuvok to work on the problem. Meanwhile, Neelix is intrigued by all the references to "spam" and replicates several dishes made with Spam. Voyager finally returns to the space station where the virus originated, and Janeway persuades the virus' designer to remove it from the ship's systems.