According to Computerworld, security firm Cenzic has released a report showing that Firefox and Safari were the least secure browsers in the first half of 2009. That's the impression you get by simply skimming the article anyway. The actual report from Cenzic only counts the number of security flaws, and concludes that Firefox had 44% of all vulnerabilities, Safari had 35%, IE had 15%, and Opera a mere 6%.
Does that really mean that IE is more secure than Firefox and Safari?
I'm not sure a conclusion like that can be drawn at all. There are other aspects to security vulnerabilities that were not covered, such as the severity, and how long the vendor takes to fix them. Furthermore, security reports sometimes elevate standard crash bugs into security bugs, for example referring to them as "Denial of Service Vulnerabilities".
It's great to see that Opera has a low number of vulnerabilities, and I am confident that we would look good if severity and "time to fix" were taken into account as well. But until the report actually includes those relevant details, it isn't really that useful.
Statistics are great, though. You can make them show just about anything.