Scientists have discovered a virus that billions of people may carry in their guts—but not to worry, it doesn't make you sick, Ed Yong reports on his blog at Phenomena. The new virus, called crAssphage, is a bacteriophage, a virus that infects bacteria; its exact role in the human body is still unclear. Researchers found it in three-quarters of 466 stool samples from the United States, Europe, and Korea, the researchers report in Nature Communications. Oh, and that slightly sophomoric name, crAssphage? That's because the team used a technique called cross-assembly to identify it, Yong reports.