While running the manual scanner, you should consider disabling real-time protection in your primary antivirus program – if only to speed things up.
When you select an additional antivirus program, look for one that doesn’t stay running in the background – this feature is referred to by many names, such as real-time protection, on-access scanning, background protection, or resident shield.
You should only run a single antivirus application at a time, but none of them are perfect.
The antivirus has a background, always-on scanning feature that’s enabled by default.
When you download a file, load a program, or access a website, the antivirus keeps an eye on everything and ensures it doesn’t match a known threat.
This works fine as long as you only have a single antivirus running at a time.
These programs hook deep into your Windows operating system and are not designed to work together.
To get more complete detection coverage, you may want to scan your computer with additional antivirus programs while leaving a single antivirus program – such as Microsoft Security Essentials (known as Windows Defender in Windows 8) — running in the background.