JR wants to know what the difference is between Windows Defender and Windows Security Essentials. Leo says that Defender is the Windows 8 version of Security Essentials, although there is an older version of Defender that's before Windows 7. For Windows 7, Leo advises staying with Security Essentials. If JR wants to pay, Eset's Nod 32 is far superior.
(Disclaimer: ESET is a sponsor).