Pwn2Own is an annual contest where hackers are pitted against different software and electronics with the goal of hacking or exploiting them in some way they should not be able to. The name basically means "hack it, keep it".
One of the biggest targets at Pwn2Own are web browsers. Since web browsers are used by almost everybody using the Internet, a lot of attention has been given to Pwn2Own in recent years. Often using exploits they had advanced knowledge of, hackers exploit browsers running on Windows, Mac OS X and Linux platforms.
Internet Explorer 8, for example, has been quite unsuccessful at Pwn2Own, which its Data Execution Protection (DEP) being beaten multiple times. Safari has also been exploited to gain control over the Mac OS X operating system.
In 2011, Internet Explorer 8 and Safari were successfully exploited again, but interestingly, Firefox and Google's Chrome browsers survived the event.
The same year, the mobile version of Safari was exploited to gain access to an iPhone address book. The handset was running iOS 4.2.1. Blackberry Torch 9800 was also compromised.
While attacks against Firefox, Android and Windows Phone 7 were scheduled, they never were tested.