Microsoft’s Internet Explorer 10 is better at blocking malware downloads than rivals Chrome, Firefox, Safari and Opera thanks to superior URL and application reputation technology, a new test by NSS Labs has found.

Browser security has been getting more and more layered and complex.  How it works and whether it works is probably a complete mystery to even the most attentive browser users but the NSS Labs study found marked and surprising differences between the most popular browsers.

After testing the latest version of each of the five browsers against 754 malware-infected URLs over 28 days, IE10 (running on Windows 8) achieved a raw block rate of 99.9 percent, ahead of Chrome’s 83.1 percent, Firefox’s 10 percent, Safari’s 9.9 percent and Opera’s 1.8 percent.

What immediately stands out is the huge gap between the effectiveness of IE and Chrome versus the weak blocking of the other three so what is going on and does it accord to real-world performance?

According to NSS, the explanation is that Firefox and Safari both use Google’s older Safe Browsing API v1, a part-cloud URL reputation system, while Opera bought in a similar scheme from a third party. Neither of these options appears to work well any longer.

Interestingly, as of late last year Chrome itself uses the more advanced Safe Browsing API v2 that offers superior protection thanks to a second layer that expands the checks performed on both files as well as URLs.

IE, by contrast, offers the same mix of URL and file reputation filtering as Chrome using SmartScreen but puts itself at the top of the blocking heap by adding a further layer, Application Reputation (sometimes called SmartScreen Application Reputation), basically a cloud scoring system for assessing each application to see whether it or its publisher is known good, known bad, or unknown.

By suspecting all applications until they meet certain criteria, App Rep seems to have better detection of malicious downloads served from previously unknown (i.e. new and potentially risky) domains.

Microsoft and Google's technologies aren't that different to one another in principle but Microsoft's appears to have found more sophisticated file-oriented analytics for spotting realworld threats.

NSS points out that the real-world performance of all reputation systems, including Microsoft's App Rep, will still depend on avoiding false positives and on end user behavior. Just because a warning is thrown up about a URL or file doesn’t mean the user will act on it.

“Regardless of the shortcomings of systems that rely upon untrained users to make correct choices, application reputation is a highly significant and effective protection technology,” said the authors.

While it might sound like a technical advantage, the effectiveness of browser security now probably matters as much to PC security as do traditional technologies such as antivirus.

“Web browsers remain the primary infection vector for most consumers and enterprises. Improving the browser’s malware block rate substantially impacts one’s security profile,” said NSS research director Randy Abrams.

The results suggested that Google’s Chrome – and the other browsers taking technology from Google – was still over-reliant on less effective reputation technology than was being used by Microsoft, he said.

“The net result is that IE 10 users are offered superior protection over Chrome users with one quarter the risk of making a bad download decision. Firefox, Safari, and Opera users are afforded little protection at all by their browsers.”

NSS Labs tested IE10's performance on Windows 8; the same App Rec system was also available to Windows 7 users running IE9 but it was unclear whether this would show the same protection, the firm warned.