"Conficker is a program that is spread by exploiting several
weaknesses in Microsoft's Windows operating system. Various
versions of the software have spread widely around the globe since
October, mostly outside the United States because there are more
computers overseas running unpatched, pirated Windows. (The program
does not infect Macintosh or Linux-based computers.)
"An estimated 12 million or more machines have been infected.
However, many have also been disinfected, so a precise census is
difficult to obtain." Look, they actually identify the vulnerable operating system!