If you're using Windows 8/8.1, the Windows Defender is there for you.
If you're using Windows XP/Vista/7, use the Microsoft Security Essential.

Microsoft Security Essential & Windows Defender is free anti-virus provided by Microsoft.
The difference between these 2 is that Windows Defender has native anti-virus pre-installed into Windows 8/8.1
While Microsoft Security Essential is an optional installation.

http://windows.microsoft.com/en-us/windows...ntials-download.

I've been using Microsoft Security Essential & Windows Defender for years.
All my PC & laptops both at home & the office has never been attacked by virus/malware/trojan until today.

This post has been edited by sHawTY: May 27 2015, 08:41 AM

Windows Defender always notifies you when they quarantined something
You might have missed the notification. Go look in the quarantined files, it'll be there, then you can choose to whitelist the activator and it'll go back to the folder where it's originally stored