We recently became aware of a device known as an IP Box that was being used in the phone repair markets to bruteforce the iOS screenlock. [...]
What is surprising however is that this still works even with the "Erase data after 10 attempts" configuration setting enabled. Our initial analysis indicates that the IP Box is able to bypass this restriction by connecting directly to the iPhone's power source and aggressively cutting the power after each failed PIN attempt, but before the attempt has been synchronized to flash memory. As such, each PIN entry takes approximately 40 seconds, meaning that it would take up to ~111 hours to bruteforce a 4 digit PIN.
4 digits: 4 1/2 days. 5 digits: 45 days. 6 digits: 16 months. 7 digits: 12 years.