Interestingly enough, by "bigger" they just mean that a larger percentage of Macs are infected compared to the percentage of Windows machines that were infected by Conficker (when compared to the total number of machines in use on each side).
What percentage of Window machines did Conficker infect? 30% 50%? I seem to remember it was a huge percentage.
"It's estimated that at its peak Conficker infected more than 11 million PCs globally."
-- http://www.sophos.com/en-us/security-news-trends/reports/sec...
Numbers in the range 15-25 million were also tossed around. It's hard to estimate.
Steve Ballmer expected the Windows installed base to cross the 1 billion mark in mid-2008: http://www.zdnet.com/blog/microsoft/microsoft-expect-windows...
Conficker peaked around January 2009 I believe. At 10 million that would be 1% of 1 billion.