ComboFix is a freeware ONLY run on Windows Vista (32-bit/64-bit), Windows 7 (32-bit/64-bit), Windows XP (32-bit only), NOT on windows 8 or Mac OS.
ComboFix will create a system restore point and backup your windows registry automatically ,you can restore back (How to Restore Your System in Windows) your system to your previous configuration if there is any problems whe you use the combofix to scan and remove malware ,spyware or virus on your windows computer.
How to Keep A Windows 8 System Safe and Secure
Windows Defender: Scan and Remove Viruses In Windows 8
How to Turn on the Firewall in Windows 8
Choosing The Best Antivirus Programs For Windows 8/8.1
How Do You Get a Virus and How Combofix Remove This Virus?