Apple has released its biggest iPhone security update yet, fixing bugs in the mobile phone's browser, mail client, and Bluetooth networking server.

The majority of the flaws do not appear to be critical, but the update fixes a larger number of bugs than the first iPhone update, released July 31.

Hackers have said that the iPhone's browser and mail clients are the most likely sources of software flaws, and this release bears that out. Apple fixed seven flaws in the Safari browser, two in the iPhone's mail client, and one Bluetooth bug with the release.

The Bluetooth flaw could be the most serious -- Apple said that it could allow an attacker to run unauthorized code on the iPhone -- but because Bluetooth works over a range of just a few feet, the attacker would have to be standing near the victim for any exploit to work, said Andrew Storms, director of security operations with nCircle Network Security.

Noted hacker HD Moore agreed that the Bluetooth flaw was serious. "The only bad issue here is the Bluetooth [flaw]," he said via e-mail. "I will start working on this tonight."

Though there may be some technical limitations to what an attacker could do by exploiting this bug, it "could be a nasty remote exploit," he added.

Earlier this week, Moore added iPhone hacking capabilities to the Metasploit hacking tool that he develops.

The patch also fixes some cross-site scripting and JavaScript flaws in the browser that could also be serious, Storms said via instant message. These flaws could be exploited to make the browser run unauthorized JavaScript code, he said.

Mobile phone users typically cannot update their own software, but Apple introduced this capability in the iPhone, which uses the update mechanism in the phone's iTunes music player.

iTunes checks for these updates once per week, so it may take up to seven days for all iPhone users to see these updates. Apple advises users to install the update immediately.