Security researcher Dino Dai Zovi stated at the Hack in the Box conference in Malaysia that ARM chips are a safer bet than x86 processors, not because they use a safer design but because fewer people are familiar with it:
Zovi, formerly of Matasano Security, isn't a high-profile figure in the industry, but he has worked on several notable projects, including the hardware-based Vitriol rootkit that took advantage of Intel's VT-x technology to infect a system. He won the April 2007 MacBook hacking contest, has presented at Black Hat, and maintains a strong interest in how processor architectures affect security.
At the Hack in the Box conference, Zovi warned that a theoretical x86 iPhone would have to deal with security problems that an ARM-based phone would not encounter. "That [the use of an x86 processor] will make the iPhone x86 and that will make a lot of attacks easier," the researcher told InfoWorld. "The iPhone uses the ARM processor and most people are not familiar with it...If you're doing exploits and vulnerability research, you need to know the specifics of the processor that's running."
Zovi did not give specifics on precisely how malware authors and hackers might exploit the x86 architecture to attack a smartphone, but he did note that the version of OS X that runs on the iPhone is "significantly" less secure than its desktop counterpart. Again, he declined to provide exact information on how the two were different.