Yes! You can use the Max Secure Anti Virus on all the operating systems on your PC. You have to just install the Max Secure Anti Virus and register it with the same registration number on each operating system on your PC. As long as it is the same hard disk and CPU it will work. If you add another hard disk, change hard disk or want to use the same registration number on another PC then it will not work.

For example :
Suppose you have Windows 2000 on C drive and you have installed Max Secure Anti Virus on this operating system. Now you are also having Windows XP on the D drive of your computer and you want to use Max Secure Anti Virus on this operating system also, then you have to just Install the Max Secure Anti Virus on this operating system and re-register the product with the same registration key provided to you.