According to an analysis from ThreatFire, 58,000 PCs running Vista were compromised by at least one piece of malware over the six months to May 2008, equivalent to 27 percent of all Vista machines probed.
In total, Vista suffered 121,380 instances of malware from its 190,000 user base, a rate of malware detection per system is proportionally lower than that of XP, which saw 1,319,144 malware infections from a user base of 1,297,828 machines, but it indicates a problem that is worse than Microsoft has been admitting to.
Source: Computer World.