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That's according to the software giant's latest Security Intelligence Report, which shows an increased rate of infection for Vista, at 3.24 percent. Windows 7 is lower at 2.59 per cent, compared to 2.42 per cent for XP.
Unsurprisingly, Windows 8 and 8.1 have the lowest infection rates of 1.73 per cent and 0.08 per cent respectively, arguably because they aren't as popular as their predecessors and therefore present a less lucrative market for the shady hacker underworld.
The figures have been normalised to reflect different numbers of computers running each operating system.
Despite the stark warning, security experts think the figures are somewhat misleading. Speaking to The Independent, security researcher Graham Cluley warned that Windows XP is still less secure than newer versions.
He pointed out that the numbers Microsoft has come up with cover a time when Windows XP was still receiving updates, and was thus more secure.
He also suggested that the popularity of newer versions is partly to blame for the increased threats, as those versions would naturally be used more often to access the internet.
Microsoft ended security support for Windows XP in April. This week's Patch Tuesday will be the first time where vulnerabilities and bugs are pointed out in the ageing OS, but not fixed, making XP a sitting duck for cyber criminals.