The security researcher who walked away with $10,000 Thursday by hacking a MacBook Air in less than two minutes said he chose to attack Apple Inc.'s operating system for one simple reason.

"It was the easiest one of the three," said Charlie Miller, a principal analyst with Independent Security Evaluators (ISE), a Baltimore-based security consultancy. "We wanted to spend as little time as possible coming up with an exploit, so we picked Mac OS X."

On Thursday afternoon, Miller breached a MacBook Air, one of three laptops up for grabs in the PWN 2 OWN hacker challenge at CanSecWest, a security conference that wraps up today in Vancouver, B.C. For his efforts, he was got the computer and a $10,000 cash prize.

The MacBook Air was running the most current version of Mac OS X, 10.5.2 with all the latest security patches applied. The other two computers, a Sony Vaio VGN-TZ37CN running Ubuntu 7.10 and a Fujitsu U810 notebook running Windows Vista Ultimate SP1, were also up-to-date and fully patched.

"We sat down about three weeks ago and decided we wanted to throw our hats into the ring," said Miller, referring to himself and ISE colleagues. "It took us a couple of days to find something, then the rest of the week to work up an exploit and test it.

"It took us maybe a week altogether," Miller said.

Because Miller was bound by a non-disclosure agreement with 3Com's TippingPoint, the security company that ponied up PWN 2 OWN's cash prizes, he was unable to share details of the vulnerability. He did confirm, however, that he had exploited a bug in Safari 3.1, the current version of Apple's browser.

The PWN 2 OWN challenge actually started Wednesday, but the rules for that first day required researchers to break into one of laptops using a remote code-execution exploit of a zero-day. At stake: the laptop and $20,000. Only one researcher stepped up that day, however, and was unsuccessful.

Yesterday, the computers' exposure to attack was expanded by allowing hackers to go after any client-side applications installed by default, including Web browsers. Contestants were also allowed to replicate the common tactic of duping a user into following a link in an e-mail or visiting a malicious Web site. In Miller's case, he had set up a malicious Web site; the URL to that site was typed into Safari's address bar.

"I've had a change of heart," said Miller today. "I used to think server-side vulnerabilities were easier to exploit, but now I almost think it's easier to exploit the client side. Think about a browser. There's a million things it has to do. It has to handle images and video and audio and ... that's where the danger is these days."

Miller, formerly with the National Security Agency, may be best known as one of the first to hack Apple's iPhone last summer. In August 2007, he also blasted Apple for its sluggish updating of the open source components it uses in its operating system, calling the practice "negligent."

At the time, Miller said he had found at least one critical vulnerability that had been patched in WebKit, the open source code that powers Safari's engine, but integrated into Apple's browser. When pressed whether the vulnerability he used yesterday to snap up the $10,000 was a similar bug, he sidestepped the question. "The version of WebKit Safari was using [before 3.1] was very very old, but when they switched to 3.1, it's now pretty much up-to-date."

Apple updated Safari to version 3.1 two weeks ago, patching 10 vulnerabilities in the Mac OS X edition, most of them cross-site scripting bugs.

"[Mac OS X] security is better than it was three or four months ago," said Miller when asked to characterize Apple's current security status. "...We were equally capable of finding [a vulnerability] in Windows if we had to," he said.

TippingPoint, which acquired the vulnerability for its Zero Day Initiative (ZDI) bug-bounty program, said yesterday that it has reported the Safari flaw to Apple. "Until Apple releases a patch for this issue, neither we nor the contestants will be giving out any additional information about the vulnerability," TippingPoint said in a statement on its company blog.