Windows Defender anti malware directly integrated into the system and antivirus Security essentials offered through Windows Update and already number one in the U.S. , Microsoft reached a new milestone in pre-installing a solution against viruses. It would have been more logical to integrate directly Security Essentials but it is a roundabout way Microsoft has chosen by modifying the Windows Defender
anti-malware for it to detect and block viruses.
There is little doubt that Defender offers the same level of protection as Security Essentials, but there are a few feature differences in the Defender software itself..in the end its a free anti-virus software available for a couple of years.

But even Microsoft has been making it to protect computers from any malwares,viruses its still not that good for that ...users need some antiviruses.
In this tutorials i will show you how Turn Windows Defender in windows 8 if you installed an other anti-Virus.
From Control panel click on
Windows Defender
Windows Defender window will open the click on
Setting tab then select
Administrator and uncheck the box
Turn on windows Defender
Windows Defender has been turned off
Your Windows Defender had been disabled. DONE