Lex uses Windows Defender, but he came across a thumb drive and wants to check it to see if it's safe to use. Leo says he really can't. If he plugs it in, and it's infected, it will compromise his system. Firmware can be modified on a thumb drive to contain malware as a payload, and it's undetectable. The worse part is not one USB drive manufacturer has done anything to correct the bug. Wired has a story on it.