In a perfect example of terrible timing, Microsoft MSFT +1.01% has published its biannual Security Intelligence Report (SIR) which shows Windows 7 and Windows Vista are infected by malware and viruses more regularly than the outgoing Windows XP . The data is likely to make Microsoft’s attempts to drag XP users to a newer operating system even more difficult.

Breaking the data down, the report states computers running Windows XP had an infection rate of 2.42% versus 3.24% for Windows Vista and 2.59% for Windows 7. The good news for users on the latest version of Windows was Windows 8 and Windows 8.1 showed infection rates of 1.73% and just 0.08% respectively.

Needless to say the figures are likely to cause outcry and a lot of ‘I told you so’ comments will be directed at Microsoft, especially as the figures were collated by the company’s own Malware Protection Engine. But they aren’t as clear cut as they would seem.

There are several crucial points to make:

1. The report covers the period July to December 2013 which means Windows XP was still supported with security updates by Microsoft. Something that officially ended (with one notable exception) in April.

2. Windows 7 and Vista were affected by an OS-specific threat from ‘Rotbrow’ malware during this period, which has now been snuffed out.

3. Windows XP still accounts for 25% of all PCs in use compared to nearly 50% of all PCs that run Windows 7 and just 10% of PCs running Windows 8.

4. Windows XP machines are be older so they are likely to be used less regularly than newer PCs.