Do I need to disable Windows Defender [FKA Microsoft Security Essentials] before I install a third-party anti-virus application or security suite?

Oftentimes, WD will disable itself, if another AV or IS is installed. If not, just go into the "Tools" section, uncheck "Use this Program", then click apply. But you'll have to manually disable the firewall to install an IS.

And welcome to the forum! Hope that you hang around & learn with us.

Best of Luck,
Cat

Yes be sure it is disabled if you are installing another AV. Often if two AV's are running in tandem they can conflict with each other as well as slowing your system down.

WD disabled itself for me, when I installed SuperAntiSpyware Pro (lifetime version). I manually disabled the firewall prior to installing ESET Smart Security 5. MBAM Pro gives me even extra protection against the real nasty stuff, plus blocks known malware sites (ESET also blocks some sites). That's 3 layers of security that doesn't conflict with one another.

Usually, WD/MSE blocks things that I know are safe, apps that may have an optional toolbar. Mabye once in a while it'll intercept something bad, this is why I have MBAM Pro installed wherever MSE is installed.

SAS, also available as a free version, catches many ad & tracking cookies (usually coming from using IE) & an occasional trojan here & there. And yet, even with these layers of security, my CPU/RAM usage is still low using Windows 8 CP. Amazing.

Cat