For several years now Microsoft started to fight non-genuine copies of Windows. Unfortunately still some legal copies are affected by the anti-piracy system.
Once you see the message above (Windows Vista or 7) reboot your system as soon as possible and once you login again, Click the Start Menu type “activate windows”.
However some users click “Get online and resolve now” link and they get a message Windows Activation:
“An unauthorized change was made to Windows. You must reinstall or restore Windows system files to activate.”
Proceed with the same procedure, reboot your PC and Activate windows.
Microsoft also recommends to uninstall programs that checks your system files such as anti-spyware and third-party firewall.
For me, anti-piracy is not needed in all version of Windows because sometimes this a good strategy for both both hardware and software manufacturer to popularize a product.
Anyway, All of us have different views but most of the time we share the same goals in groups. So if you have some suggestions please post to the comments below. Thanks!