The security experts at Trend Micro have crowned Apple's Mac OS X as the riskiest operating system to be used based on the long patch cycles. There was a huge 644 MB patch sent out last November, five months after the previous patch. Trend Micro pointed at the sheer size of the update, but noted that " Apple’s penchant for secrecy and longer patch cycles also increased the risk for users."
There was not any more information for the honor, but we would think that Apple may be anyway at greater risk as Mac OS X is capturing greater market share and popularity. Security, and is especially the perception of a secure operating system, may be something that Apple will have to take much more serious in 2011.
Trend Micro also mentioned WordPress as the most dangerous software of 2010, IRC as the most dangerous IP protocol, Google as the most dangerous website due to its gateway role to malware threats, Facebook as the riskiest social network site, PDF as the worst file format, IE as the most dangerous runtime environment, the web browser as the main malware infection channel, and CO.CC as the most dangerous top-level domain.