BitDefender Antivirus Free Edition is the free antivirus and anti-spyware protection for Windows. It uses the cloud to provide real-time protection of Windows systems using the same scanning engine and protection that is built-into the commercial products.
You can turn the virus shield on or off, and select whether you want the program to auto scan the system when it is idle. Note that you need to register an account with My Bitdefender to use the program after 30 days of use.
Here is a short video that demonstrates how it performs against malware attacks.
Bitdefender Antivirus Free Edition is compatible with all recent versions of the Microsoft Windows operating system.
Note: It will remove other security software installed on the system if you are not careful during the installation. You may also want to disable the anonymous usage report generation if you prefer not to send data to the company.