Windows XP PC shows "you may be a victim of software counterfeiting"

There should be other data with that statement as well as a number to call Microsoft. Write it down and make the call. If Microsoft is satisfied your copy of XP is legitimate they will give you a code to enter which will make the message go away. Sometimes their anti-piracy program makes errors. I am assuming you have a valid copy of the OS. Good luck. Ralph

It's best to do the re-activation by telephone, not via internet. They can sort out problems pretty well.