With the large number of web applications for the iPhone, Apple lists more than 600, the Mobile Safari browser plays a large role. Recently a Denial of Service(DoS) vulnerability was discovered in iPhone’s web browser.
The researchers who found the vulnerability were looking for a method to unlock the filesystem on iPhones with the latest firmware(1.1.3). Unlocking the filesystem allows the installing of custom ringtones and 3rd party applications. With the last firmware version you could automatically unlock your iPhone by visiting a particular website with the Mobile Safari browser.
Computer Security Research - McAfee Avert Labs Blog