Windows Defender is a free antimalware program that comes preinstalled with the Windows Vista and 7 operating systems. By running Windows Defender, you can remove malicious programs that have infected your operating system. Unfortunately, some malicious programs are actually designed to prevent you from accessing your security programs. If your computer is infected with one of these malicious programs, you can use the Windows Command Prompt to run Windows Defender.
Click "Start," "All Programs," "Applications" and "Command Prompt." The Command Prompt opens.
Type "MpCmdRun.exe -Scan [-ScanType]" (without the quotation marks). Note that "-ScanType" should be replaced with one of the following numbers, depending on the type of scan you want to run.
0: Default scan according to your current configuration 1: Quick Scan 2: Full system scan
Press "Enter." Windows Defender will now scan your computer. When you are done with the Command Prompt, type "exit" (without the quotation marks) and press "Enter."