Infection Rates of Windows Operating Systems

The latest Microsoft Security Intelligence Report (SIR) has been released. It provides an in-depth perspective on the changing threat landscape including software vulnerability disclosures and exploits, malicious software (malware), and potentially unwanted software. Using data derived from hundreds of millions of Windows users, and some of the busiest online services on the Internet, this report also provides a detailed analysis of the threat landscape and the changing face of threats and countermeasures and includes updated data on privacy and breach notifications. The sixth volume of the report is now available:

SIR Volume 6 (July through December 2008) and Key Findings Summary (available in 10 languages)

One important analysis is that the malicious software infection rates differ significantly for different versions of the Microsoft Windows operating system. Windows Vista was less infected at any service pack level than Windows XP. Comparing the latest service packs for each version, the infection rate of Windows Vista SP1 is 60.6 percent less than that of Windows XP SP3.