Microsoft's Internet Explorer 9 (IE9) blocks more malicious sites and malware than any other browser, including its predecessor IE8, according to a report released Tuesday.
The still-in-beta browser was five times more effective at warning users of potential danger than its closest rival, Mozilla's Firefox, said NSS Labs, which conducted a Microsoft-commissioned study of browser anti-malware tactics and technologies. IE9 also beat Microsoft's current production browser, IE8, by nine percentage points.
Microsoft claimed that IE9's improved score was due to the addition of SmartScreen Application Reputation, a new feature that uses a complex algorithm to rank the probability that a download is legitimate software.
"We wanted to look at malware blocking from a new perspective," Jeb Haber, principal program manager lead for IE security, said in a Tuesday interview. "We looked at what people are downloading [via IE] and found that a significant percentage of executable files were later confirmed to be malware."
Application Reputation, or "App Rep," uses a file's hash -- which identifies the file contents -- and its digital certificate to determine whether it's a known application with an established reputation. For example, "firefox.exe" would be labeled a legitimate download with a known history and reputation. If the App Rep algorithm ranks the file as unknown -- perhaps because the hash value hasn't been seen before -- IE9 throws up a warning when users try to run or save the file.
Haber refused to call App Rep a "whitelist" -- the term for a pre-approved list of allowed software -- saying that it was more accurately an "allow" model since users can click through the warnings and still install software that triggers a warning.
Microsoft started serving App Rep data to IE9 Beta in October.
Haber said Microsoft sees App Rep as a way to "close the gap" that remains in browser-based anti-malware technologies, which generally just interpose a warning between the time users click on a potentially risky link and when the site renders.
NSS Labs attributed the bulk of IE9's improved score over IE8 -- which offers anti-malware blocking through SmartScreen Filter -- to App Rep. At a minimum, said Rick Moy, president of NSS Labs, five of the nine percentage points that IE9 scored over IE8 can be credited to App Rep.
"Reputation matters," said Moy, "and [App Rep] is pretty darn compelling."
IE9's App Rep warns users when it suspects that a downloaded file is dangerous.
But Moy also gave kudos to Microsoft's decision to put money and muscle behind browser blocking. "The obvious question is why does IE do such a good job?" asked Moy. "It's clear that the others just aren't putting the same amount of resources into solving the problem of malware and social attacks. The data bears that out."
NSS tested six Windows browsers -- IE8, IE9 Beta, Firefox 3.6, Safari 5, Chrome 6 and Opera 10 -- against socially engineered malware: Sites that dupe visiting users into downloading attack code. Typically, the download is disguised, often as an update to popular software such as Adobe's Flash Player, or as an innocuous video codec.
The tests did not include sites that attack browsers without any user interaction via drive-by attacks that exploit known or unknown vulnerabilities in Windows or its applications.
According to NSS Labs, IE9 blocked 99 per cent of the 636 malware-distributing sites that were included in the final data. IE8, meanwhile, blocked 90 per cent. Firefox warned users of just 19 per cent of the same sites, while Safari, Chrome and Opera stymied 11 per cent, three per cent and zero per cent, respectively.
IE has taken honors in previous Microsoft-sponsored tests run by NSS Labs, but its scores, particularly IE9's, have improved significantly. Rivals' efforts at blocking malicious sites, however, have seriously degraded.
Although Firefox, Safari and Chrome offer anti-malware blocking -- the three rely on Google's own SafeBrowsing API -- their scores dropped between 10 and 14 percentage points since NSS Labs last tested them in early 2010.
"There's the [Microsoft] SmartScreen camp, and then the Google SafeBrowsing camp," noted Moy. He credited the different results among Firefox, Chrome and Safari to their different implementation of the SafeBrowsing API.
But looking at his testing data, Moy said it was clear that IE was head and shoulders, and then some, above the competition.
"Microsoft's not only using the blacklist approach [to warn users of possible malicious sites] but it's also bringing its knowledge of good applications into the data feed," Moy said. "Look at IE9 ... it's darn near perfect [on the tests]."
IE9 requires Windows Vista or Windows 7 , and can be downloaded from Microsoft's site. The release candidate, or RC build, of the browser is slated to ship in early 2011 , but Microsoft has not yet set a final release date.
NSS' malware blocking test report can be obtained from Microsoft's site as well ( download PDF ).