According to a new Security Intelligence Report by Microsoft, 9.1 out of 1000 Windows XP SP3 PCs are infected by malware - roughly six times higher than the infection rate found on Windows 8 machines.
The Microsoft Security Intelligence Report takes data from over one billion sources across the Windows landscape – data was drawn from Redmond real estate such as its Malicious Software Removal Tool, Exchange Online, Windows Defender and more – providing an overview into the threat landscape across Windows boxes around the world. The information was collected during the first six months of 2013.

Source: The Register