The Mac vulnerability found as part of a $10,000 hacking contest is actually a QuickTime bug, and it works on Windows machines too.

The vulnerability that surfaced last Friday is "very serious" and can be exploited through any Java-enabled browser, including Internet Explorer 7 running on both Windows XP and Vista, the company that laid out the prize has revealed.

Unconfirmed reports also claimed that someone may have captured the exploit on Friday as the MacBook Pro was attacked. If that turns out to be the case, a widespread attack would be more likely.

Although the bug was first ascribed to Apple's Safari browser, by Monday researchers at 3Com TippingPoint, which put up the prize money as part of its Zero Day Initiative bug bounty program, had confirmed the vulnerability was in QuickTime.

Because the flaw is in QuickTime's code, and because QuickTime plug-ins are commonly installed on both Macs and PCs and with all major browsers, the attack surface is "huge," said Terri Forslof, TippingPoint's manager of security research.

"This is every bit as dangerous as any vulnerability we see out there," said Forslof, who confirmed that using IE 6 and IE 7 on Windows XP SP2, as well as IE 7 on Vista, could lead to an exploit. "If Microsoft was rating this, it would [rate it as] a critical vulnerability. One click and you're owned."

"The vulnerability is in QuickTime, but any Java-enabled browser can be an exploit vector. No exclusions," said Forslof. TippingPoint confirmed this morning that IE 7 running on Vista - the browser that Microsoft touts as its most secure - could be a route to a PC hijack.

A successful exploit would require that the user be tricked into visiting a website containing malicious Java code. That kind of attack is commonplace, with links typically delivered via spam email. Until Apple patches QuickTime, the only sure defence, said Forslof, is to disable Java in the browser.

Late this morning, researchers at Matasano Security, the New York-based consultancy where the MacBook contest winner, Dino Di Zovie, once worked, said it had unconfirmed reports from credible sources that the exploit had been snatched out of the air at the CanSecWest conference.

The MacBooks left open to attack during the CanSecWest challenge were connected to an unprotected wireless network, said Matasano's Thomas Ptacek in a blog this morning. "Raw packet captures of the successful exploit have been taken by parties unknown," he said. "There's a difference between the exploit being captured and the exploit being successfully hosted by attackers in the wild....[but] even so, this is a particularly virulent problem."

Adding fodder to those reports, a writer on the Information Security Sell Out blog claimed to have not only captured all data packets transmitted during the hacking contest, but had reverse-engineered the vulnerability.

Ptacek of Matasano, however, was dubious. "Their claims aren't corroborated by any of the public record about the vulnerability, which, contrary to their report, doesn't appear to involve 'the way QuickTime handles Javascript'."

Forslof would neither confirm nor deny the reports of the exploit - for which it paid Di Zovie the $10,000 - escaping into the wild. "We're keeping the details of the vulnerability close to the chest," she said, "but QuickTime is pretty ubiquitous. With so much press around the actual challenge and so many people interested in it, an exploit is just a matter of time."

Although Forslof said that her team had reported the QuickTime vulnerability to Apple on Monday, the computer maker has refused to comment on the specifics of the bug.

Company spokesman Anuj Nayar would only repeat the standard Apple statement issued when security questions were asked: "Apple takes security very seriously and has an excellent track record of addressing potential vulnerabilities. We always welcome feedback on how to improve security."