Pwn2Own 2010 is a contest to find security vulnerabilities in various operating systems, one of the best security experts, Charlier Miller, speaks about the different OSes and their strenghts and weaknesses.
He compares Mac OS X and Windows 7, the mobile platforms like Android and iPhone OS as well as Linux.
Comparing Mac OS X and Windows 7, Charlie Miller claims that Windows 7 is more secure than Mac OS X, most vulnerabilities are due to browsers and advices to not install Flash.
“Windows 7 is slightly more difficult because it has full ASLR (address space layout randomization) and a smaller attack surface (for example, no Java or Flash by default). Windows used to be much harder because it had full ASLR and DEP (data execution prevention). But recently, a talk at Black Hat DC showed how to get around these protections in a browser in Windows.”
Source: One IT Security via VRZone