Guys how would we know if an operating system is not a genuine
software?

I had certainly encounter some problem with my XP software, everytime
i go online in the net a message will always show up stating that "You
may be a victim of software counterfeiting", does this mean that the
software i had purchase is not a genuine software?

How would i resolve this problem? If indeed my software is not a
genuine one, will i able to return this to the seller?

Please help me with this. Thanks.