Which software is it that announces it is 'Counterfeit'?
If it is the operating system XP PRO
Then you will have to reformat the disk and purchase a new copy.
In the announcement you will see put this right now. click on that and Microsoft will come up and say words to the effect- You can make this legal by passing us a sum of Money- at which point you get your flexible friend out
Simply ignore it - notwithstanding all the threats the Software police are not likely to knock on your door.
If it is simply some other software go to Start/Control Panel/Add Remove software
Highlight and the offending item and click delete