If you are a new PC user, and haven’t got the protection you need to defend against malware, then MSE is a great malware defender that can be combined with spybot search & destroy and also malwarebytes. The best thing about this tool, is that it is freeware and does a great job in detecting malware and backdoors. MSE should not be installed with any other antivirus program like Eset or ZoneAlarm because conflicts can occur. This tool seems to run quite and efficient in the background if your ram is a good amount (around > 3GB) and shouldn’t be a problem with any slowdowns.
Windows 64 bit: http://mse.dlservice.microsoft.com/download/A/3/8/A38FFBF2-1122-48B4-AF60-E44F6DC28BD8/enus/amd64/mseinstall.exe
Windows 32 bit: http://mse.dlservice.microsoft.com/download/A/3/8/A38FFBF2-1122-48B4-AF60-E44F6DC28BD8/enus/x86/mseinstall.exe