Update (6/18): Microsoft Based on the recently leaked build, Ars reports that MSE has separate installers for Windows XP, Windows Vista, and Windows 7 in both 32 and 64-bit flavors. File sizes are also rather small, ranging from 3 MB to 7 MB. The security software will completely replace Windows’ built-in Defender, and should offer real-time protection against viruses, spyware, rootkits, and Trojans. Although Microsoft Security Essentials is already being tested internally, the company is expected to offer a public beta “soon,” and have the final version ready later this year.