A newly discovered virus has been found by a San Diego State University team to live inside more than half of all human gut cells sampled. Exploring genetic material found in intestinal samples, the international team uncovered the CrAssphage virus. They say the virus could influence the behaviour of some of the most common bacteria in our gut. Researchers say the virus has the genetic fingerprint of a bacteriophage - a type of virus known to infect bacteria. Phages may work to control the behaviour of bacteria they infect - some make it easier for bacteria to inhabit in their environments while others allow bacteria to become more potent. [Study lead Dr. Robert] Edwards said: "In some way phages are like wolves in the wild, surrounded by hares and deer. "They are critical components of our gut ecosystems, helping control the growth of bacterial populations and allowing a diversity of species." According to the team, CrAssphage infects one of the most common types of bacteria in our guts. National Geographic gives some idea why a virus so common in our gut should have evaded discovery for so long, but at least CrAssphage finally has a Wikipedia page of its own.