During Google's Pwnium contest at the CanSecWest security conference in Vancouver on Wednesday, Russian bug hunter Sergey Glazunov demonstrated a Chrome exploit that completely defeats the browser's much touted security sandbox.Chrome is viewed as one of the most secure Web browsers by the security community, primarily because of its sandboxed architecture, which restricts how it interacts with the OS and significantly limits what attackers can do if they exploit a vulnerability.A panel of security experts from Accuvant and Coverity, who analyzed the defensive capabilities of modern browsers in depth, said last week at the RSA security conference in San Francisco that Chrome's sandbox prevents processes from doing much of anything on the system.However, there is a consensus in the security community that while sandboxing is a strong anti-exploitation mechanism, it does not provide a perfect defense and a determined attacker can theoretically defeat it, although with a lot of work.For this year's CanSecWest conference, Google decided to run a contest called Pwnium in parallel with TippingPoint's well known Pwn2Own contest, which rewards security researchers for finding and exploiting unpatched remote code execution (RCE) vulnerabilities in browsers.Pwnium has a maximum prize pool of US$1 million and rewards various types of Chrome exploits. The largest prize is $60,000 and is awarded to researchers who demonstrate persistent RCE exploits that target only vulnerabilities in Google Chrome's code.The first to earn this top reward was Sergey Glazunov, a regular Chrome bug hunter, who on Wednesday, during the first day of the contest, demonstrated an exploit that completely bypassed Chrome's sandbox.The exploit was validated by the Google Chrome team. "Congrats to long-time Chromium contributor Sergey Glazunov who just submitted our first Pwnium entry. Looks like it qualifies as a 'Full Chrome' exploit," Sundar Pichai, Google's senior vice president for Chrome, said via his Google+ account. "We're working fast on a fix that we'll push via auto-update."Other Chrome security engineers, like Justin Schuh or Chris Evans, expressed their excitement about the exploit via Twitter. "What a great bug from Sergey. But still a whole ton of cash left, hoping for more entrants," Evans said on his Twitter feed.Glazunov, who has earned many rewards for finding Chrome vulnerabilities in the past, wasn't at CanSecWest in person. Instead he submitted his Pwnium entry through independent security researcher Aaron Sigel.During day one of the Pwn2Own contest, a team of researchers from French security firm VUPEN Security also managed to hack Chrome. However, Chrome's security team suspects that the researchers' exploit targeted a vulnerability in the Flash Player plug-in that comes with the browser by default.If that's true, VUPEN's exploit would have only qualified for a Pwnium consolation prize of $20,000, had it been submitted to the contest. VUPEN didn't confirm that their Pwn2Own Chrome exploit targeted a Flash Player vulnerability, which isn't prohibited by the Pwn2Own contest rules.