Today is the day that Microsoft's Windows XP reaches "EOL" (End of Life) status. That means they won't be issuing any more updates for it. If security researchers (good guys), or hackers (bad guys), find vulnerabilities with it, Microsoft won't be issuing a fix for them.
This has been widely covered in the media. Apparently, a third of computers worldwide still use XP. … Read more about The end of Windows XP - a money-grabbing exercise?