You're likely already infected with a brain-eating virus you've never heard of

There's a virus you may have never heard of before that is estimated to infect up to 90 percent of people and lurks quietly in your cells for life—but if it becomes activated, it will destroy your brain. If that's not startling enough, researchers reported this week that there may be a new way for this virus to activate—one that affects up to 10 percent of adults worldwide.

The virus is the human polyomavirus 2, commonly called either the JC virus or John Cunningham virus, named after the...