Let me guess in the future 2011 PC World report, 2010 was a bad year for pc security. Every year is a bad year for security nothing has changed.
The reason, many people fail to use a degree of common sense, fail to learn from the mistakes they have made in the past and haven't secured their systems. Some people are repeatedly infected time after time after time, we even see it here on the forums, with some making repeated returns with infected systems.