Like I12, I've been using MS Essentials and love it (go figure, a M$ program I like!). It doesn't slow anything down, and I have yet to run into a problem. I also run Spybot Search & Destroy in the background to prevent malware. It's also recommended.
Would you recommend a program like Spybot or Malware Bytes in addition to Microsoft Security Essentials or MS Essentials is enough on it's own?
