Keith got bit by a computer virus and it corrupted the Master Boot Record. Leo says that's pretty scary because even if he wiped his hard drive and started over, the virus may still be there. Can the virus infect an external USB drive? Leo says no, unless he made it bootable. The irony is, we don't use Master Boot Records anymore -- they're a holdover from a bygone era. He'll want to be sure all his apps are up to date. Browsers, readers, Windows, the works. He can keep his antivirus updated too. Keith should still remember his best defense is his own online behavior.