Microsoft Security Essentials is a free antivirus program which can optional installed for Windows XP (32 Bit), Vista and 7. For Windows 8.1 it is integrated into the Windows OS as part of Windows Defender. Offline definitions are also listed for both products.
An offline bootable version known as Windows Defender Offline is in particular useful as a bootable Windows Defender Offline USB can be prepared on a working system and booted from in a problem system. As Windows Defender is launched out with Windows there is less chance of malicious code designed to run on Windows startup to get a footing; usually the first thing malicious code does is disable/interfere with Windows Defender and other security products on Windows startup therefore Windows Defender Offline has a much higher chance of removing the Malware as the Malware cannot disable it.
Windows Vista/7
- Windows Defender Offline Guide [Free]
- Microsoft Security Essentials [Free]
- Microsoft Security Essentials Latest Definition 32 Bit [Free]
- Microsoft Security Essentials Latest Definition 64 Bit [Free]
Windows 8.1
- Windows Defender Offline Guide [Free]
- Windows Defender [Inbuilt*]
- Windows Defender Latest Definition 32 Bit [Free]
- Windows Defender Latest Definition 64 Bit [Free]
- How to Add a "Windows Defender" Cascading Desktop Context Menu in Windows 8.1 Guide – EightForums [EightForums**]
- How to Add "Scan with Windows Defender" for Files and Folders in Windows 8.1 Guide – EightForums [EightForums**]
* Can be accessed from all programs on the start screen and has the capabilities of Security Essentials.
** These workarounds make it easier to find Windows Defender within Windows 8.1 but aren't perfect; Microsoft removed such menus from Windows Defender which were convenient in Security Essentials.