A "brute force" attack on an iPhone can cycle through nine password guesses per second, according to Dino Dai Zovi, an independent security consultant and notorious Apple hacker.
-A password made up of 4 numeric characters would take 18 minutes to hack
-Alphanumeric characters are trickier. A password with 4 of them would take 51 hours to break.
-5 alphanumeric characters: 8 years
-8 alphanumeric characters: 13,000 years