This is what the pop up looks like. This is the only version I have seen thus far. It shows up this way in Google's Chrome browser. I haven't seen up yet anywhere else on the few XP platforms we have left on client sites.
Starting tomorrow, March 8th 2014, Microsoft will begin pushing out warnings to Windows XP users that the OS will no longer be supported after April 8th this year. The pop-up will appear on all systems as part of normal patching. The message should read “Windows XP End of Support is on April 8th, 2014. Click Here to learn more”. Here is an article on the subject; http://techwindowz.com/windows-xp-end-of-support-message-to-start-popping-up-on-saturday/
Although this looks like a scary pop up it isn’t an immediate or major issue for many Win XP users. What this means to XP users is that MS will no longer supply security and Operating System patches for this OS. It won’t just stop working overnight. Over the next few months to a year it will render your systems more vulnerable to attack by hackers, viruses, and malware. Although it may not be necessary to update now, it will be in the near future so start planning ahead.
However, if you are in the medical industry or accepting credit cards on an XP computer you will need to update your systems right away. Credit card companies, Point of Sale systems, and industry standards for financial and health systems will be required to leave Windows XP behind. There is still time to get the more familiar Windows 7 OS to replace them.
This is a pop up message from Microsoft, it is not a scam. That said, the potential for abuse is massive. It will not be long before malware/virus writers and hackers begin making phony versions of this pop-up. My suggestion is that, when and if this comes up, click the “Don’t show this message again” check box and make a physical note on each machine you've updated. It is unlikely that Microsoft will send this out multiple times so if you've noted the machines its addressed you can hopefully avoid clicking on a fake pop-up in the future.
Please read this article on the subject; Windows XP end-of-support message to start popping up on Saturday