Best FREE Ad-ware and virus scan software?

[vdubsta]

I'm not so Tech Savvy, and confused about all this ad-ware and virus scan software, is there anything else I need to fully protect my computer.  All help is appreciated.  Thanks. 

 

[18key]

Malwarebytes.

 

[gregbutler20]

avast

 

[justscoreda100]

Microsoft Security Essentials is the easiest to use and it runs faster then other AV programs.

 

[cincoseisdos]

ad-aware

 

[angeezy]

check download.com