Do I need Windows Defender on if I have Avast Anti-Virus?

Hello TriciaKnight,

You don't need both on your system. You only need one anti virus application. Regardless of which third party (i.e., not Microsoft) anti virus application you choose it will always turn Windows Defender off to prevent conflicts. In answer to your question "will it cause a conflict between defender and avast running simultaneously" the answer is Yes it will.

This forum post is my own opinion and does not necessarily reflect the opinion or view of Microsoft, its employees, or other MVPs.

You are welcome, Patrick.

It is a pity Microsoft still kept the name Windows Defender for use in Windows 8; it does cause a lot of confusion.

Here are the links explaing the difference:

http://www.microsoft.com/security/pc-security/windows8.aspx

In Windows 8, Windows Defender replaces Microsoft Security Essentials. Windows Defender runs in the background and notifies you when you need to take specific action. However, you can use it anytime to scan for malware if your computer isn’t working properly or you clicked a suspicious link online or in an email message.

And this is for Windows Defender in Vista and Windows 7:

http://windows.microsoft.com/en-us/windows/turn-windows-defender-on-off#turn-windows-defender-on-off=windows-7

When Windows Defender is on, you're notified when spyware or other potentially unwanted software tries to install itself or run on your computer. If you use the default settings, Windows Defender also checks for new definitions (files that are used to determine if software is spyware) and automatically removes any detected item that has a recommended removal action.

It is almost as bad as confusion between Office Outlook and  the new Outlook.com replacing Hotmail. :)

Cheers.