Earned a DISMAL rating at PCWorld. CONS Very poor aggregate score from independent labs. Poor score in our hands-on malware blocking test. Dismal score against downloads from malware-hosting URLs. So-so phishing protection (supplied by Internet Explorer). BOTTOM LINE Windows Defender tries to protect your Windows 8 or 8.1 installation if you don't have third-party antivirus installed. Testing reveals that you'll be much, much better off installing almost any other free antivirus utility. http://www.pcmag.com/article2/0,2817,1926596,00.asp Hopefully this debate is over. There are other better free options. In the free realm, I recommend looking at Avast, Bit, Panda & Avira. I do not recommend dirty Qihoo nor Ad-Aware. -Frank Edit: Got a PM asking me about Avira. I forgot about Avira. Adding Avira.