Microsoft Security Essentials is designed to have minimal impact on your PC's performance.
Symptom
Your computer runs more slowly than expected when Microsoft Security Essentials is running.
Cause
Antivirus and antispyware software might cause your PC to slow down, even if the software itself isn't the cause of the slowdown.
Solution
Visit the Microsoft Security Essentials website and check if your PC meets the minimum system requirements stated there. Consider upgrading your PC if it doesn't meet the requirements or uninstall Microsoft Security Essentials.
Completely uninstall any existing Internet security programs by following the steps in the topic How do I uninstall antivirus or antispyware programs?
Restart your PC.
Install Microsoft Security Essentials again. If this doesn't resolve the issue, continue to the next step.
Caution:
When you remove Internet security programs, your PC is unprotected. If you have problems installing Microsoft Security Essentials after you remove existing Internet security programs, contact Microsoft Security Essentials immediately by submitting a case online. For more information, see Submit a support case.
Download Microsoft Security Essentials now.
Close any open programs and then restart your PC.
