While schools rightly fear break-ins to their computer systems by professional criminals, students are increasingly giving educators almost as much to worry about. Reports of students' gaining access to school networks to change grades, delete teachers' files, or steal data are becoming more common, experts say, and many districts remain highly vulnerable to costly and disruptive attacks. Cyber security is a full-time job, and many districts, especially smaller ones, do not have enough staff or money to adequately secure their networks against all potential threats. The "anywhere, anytime" accessibility of many networks can be tempting to students, who can penetrate them from both their school and home computers. Unlike 10 years ago, moreover, people do not have to be true computer geeks to become hackers. Online chat rooms, listservs, and Web sites that give step-by-step directions on how to hack make it easy for students--and anyone else--to tap into networks rich with confidential data. In addition, as more districts centralize academic and other information to make data-driven decisions--as encouraged under the federal No Child Left Behind Act--they may leave themselves even more open to cyber criminals if they do not also build strong virtual fences around their networks.