"To say a system is secure because no one is attacking it is very
dangerous," said Gates,
referring to operating systems that have a smaller share of the desktop
market, such
as Apple's Macintosh OS and the open-source software Linux.

But patch management continues to be the largest headache, Gates said.
"Everybody who had their
software completely up-to-date (during the epidemics) was immune to
those problems. But only 20
percent of our customers were, so obviously, we weren't doing enough."

Hmmm - My Mac OS X server has survived attacks directed at UNIX that
were successful against
various other UNIX servers around here a number of times.  According to
Gates, no one is attacking it.
The last time I checked the goal of most attackers was to take over
Unix systems, not Windows
computers, because they were more useful once hijacked.  The "attacks"
against OS X continue
on a regular basis, they just don't succeed.