(Eugene, OR) -- Four international students at the University of Oregon could be losing their visas. One student had their visa revoked in late March and three more students are under investigation. The Department of Homeland Security says they're under investigation for criminal charges, but the details of the investigation haven't been released. The U of O has nearly 800 students with an F-1 visa. If the students lose their visa, they have 15 days to find a legal pathway to remain in the country, or they have to leave.