Your system is not virused! The message is perfectly normal! The reason for the message is that your Windows XP is counterfeited or was never registered with Microsoft.
Here is the easiest way and it is certain to work:
Go through the following steps:
*Buy the license first.
*Download Key Update Tool, a utility provided by Microsoft to change the key of the Windows version installed.
*The download address is http://go.microsoft.com/fwlink/?LinkId=50346&clcid=0x409
*Double-click the utility will then check the system files.
*Enter the official key and click Next.
*Accept the license agreement and click Next.
*The key is legalized.