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It really depends on what you do in the Windows VM. I run commercial software (not available for OS X) and never run a browser or mail, nor do I download and run dodgy software. No AV programs and I've never gotten a computer virus.
 
With the new forms of ransomware being distributed, I definitely would.

HitMan Pro
Kaspersky
BitDefender

Any of those three are great choices for keeping you safe in real time.
 
Microsoft Security Essentials is enough for the limited exposure my VM has. Free and light on system resources. Would recommend ESET if you are running for normal browsing, email, etc
 
Well, Windows shall always remain Windows, full of malware and viruses.

I take no chances, even though I keep my VM isolated as much as possible in VMware Fusion 6.

I use Norton 360 Premier Edition.
 
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