One very interesting pattern I observed in poking at [the Styx] exploit pack -- and others recently -- is the decreasing prevalence or complete absence of reported infections from Google Chrome users, and to a lesser extent users of recent versions of Mozilla Firefox.
Is it possible that the geeks in Mountain View have found the secret formula to building a more secure browser, or are there other forces at play? Most likely it's a confluence of factors, some engineered by Google, and others not.
In his blog post, Krebs provides one explanation for his observation: Adobe Reader is a common target of exploits, but recent versions of Chrome (and Firefox) include an alternate, built-in PDF parser. That means Reader never loads for most users of these browsers, rendering attempts to attack the ubiquitous application harmless.
Another piece of the puzzle is the silent automatic updater that has been built into Chrome since it launched. This ensures that few Chrome users run outdated browser versions, which harbor known vulnerabilities. Firefox introduced a similar update mechanism last year.
The browser market may provide some clues, as well. It is my observation that technically sophisticated users are disproportionately likely to use Chrome. (I haven't found any data to back this up; if you know of any, please share in the comments.) Techie users are also more likely to have their systems patched and to have Java disabled, both of which decrease their likelihood of becoming victims of drive-by downloads.
Speaking of the browser market, Chrome has far smaller market share than Internet Explorer, meaning criminals likely put less effort into attacking it. Consistently, we've seen the most popular platforms and applications (e.g., Windows, Adobe Reader, Adobe Flash, Java) get targeted most heavily by malware and exploit kit authors.
Of course, let's give credit where credit is due. Chrome does have some solid security engineering and features that effectively protect users from Web threats. In-browser warnings leverage Google's Safe Browsing API to warn users of known exploit and phishing sites. (Firefox and Safari also use the Safe Browsing API.) Each tab in Chrome runs in a separate process that is sandboxed to reduce the risk that an exploit from one site will affect other sites or the host operating system. And, like recent versions of Firefox, Chrome prompts users before running known high-risk plug-ins.
Together, these factors make a compelling case for Chrome as a browser of choice for security-conscious users and organizations, with Firefox not far behind. Of course, the threat landscape naturally shifts over time. There is no guarantee that Chrome and Firefox will lead the pack a year or two from now. And with real-time search integrated into the address bar and a liberal policy toward third party cookies, Chrome's level of privacy protection has come under fire.
Still, the conditions are aligned for the browser from Mountain View to gain extra attention from security practitioners in the coming months.