For many years, researchers mistook viruses known as giant viruses — which are 100 times larger than typical viruses — for bacteria, Carl Zimmer says at Discover's The Loom blog. But on closer examination, researchers found that despite their unusual size, these large viruses work much like typical viruses, infecting hosts and building new copies of themselves. Since they were "unveiled" seven years ago, researchers have debated the origins of these giant viruses, Zimmer says. "Many of their genes are different from those found in cellular life forms, or even other viruses.