Look at these stats on Symantec's site.
Its from their online securitychecker:
Hacker Exposure Check 19% At Risk
Windows Vulnerability Check 13% At Risk
Trojan Horse Check 4% At Risk
Antivirus Product Check 24% At Risk
Virus Protection Update Check 9% At Risk
I know they MIGHT have played a little with the stats, but then again - it might be true
