Coding Horror

programming and human factors

This Site May Harm Your Computer

The Ghost In The Browser: Analysis of Web-based Malware (pdf) describes how Google is leveraging their overwhelming search dominance to combat browser malware installations. In a blog entry last summer, Matt Cutts said:

Given how much I hate web pages that install malicious software or abuse browser security holes, I'd like it if we did even more to protect our users.

Apparently, they've done even more to protect users since then. Here's a Google search result tagged with the ominous warning "This site may harm your computer":

Search results page with an entry tagged 'this site may harm your computer'

Clicking "This site may harm your computer" leads to a Google support page. Attempting to click through to the actual website results in an interstitial warning, offering no way to click through:

Warning - vsiting this site may harm your computer!

I think this is a fairly effective method of warning away most rational users from a clearly evil website. Of course, users who desire whatever media, software, or pornography the site is hawking can still type the URL in their address bar. Users will find a way to see the dancing bunnies if they really, really want to, no matter how many warnings and barriers you blast in front of them.

If you want to see what's behind that URL, fair warning: in addition to being outright dangerous for a machine that's not patched to the gills, it's NSFW in a big way. A little investigation showed that it's doing the following:

  • Attempts to use the remote data services ActiveX control.
  • Shows a spoof HTML page with the text "windows media player cannot play video file; Click here to download missing Video ActiveX object". The download runs setup.exe.
  • Runs Javascript with exploit sniffing code.

If you accept that Google wields the immense power of being the de-facto start page for the internet, then maybe this kind of policing effort comes with the territory. To do nothing-- to let these purely evil sites show up in Google results with no warning whatsoever-- would be irresponsible. Although a person might be performing questionable searches to get this page in their results, it's irrelevant. Despite the individual ethics of the person using that one computer, a compromised computer will be used for attacks and spam against everyone.

Still, I'm a little curious. Why does Google deploy the ultimate weapon of search delisting on sites using black-hat SEO techniques to game search rankings, while known evil malware sites get stern warning interstitials instead? I brought up the Google result by doing a direct search on the domain name. The very same search produces no results on or Clearly that site has been delisted by everyone except Google. The domain still has a PageRank of four. I applaud the effort, but what value does keeping a site like that in your search index have for users?

Even if your web site is not evil, it's possible for others to inject malicious code into your page if you're not careful. The Google whitepaper provides three external vectors that can turn a good web page to the dark side:

  • Compromised webservers can insert malicious code into all HTML pages served
  • Pages which allow user-contributed HTML, where the HTML hasn't been properly sanitized
  • The use of questionable advertising content, or compromised ad servers

It's scary how many ways this can happen. I strongly urge you to read the whitepaper to get all the gory details.

Google's paper says one in ten webpages contains malicious code. The most direct way to address malware delivered via web pages is to increase the security of the operating system and the browser, so "drive-by downloads" cannot happen without the user's explicit consent. But a problem as large as malware should be attacked on multiple fronts. Search engines are in a unique position to help index and identify malicious webpages, and prevent them from being accessible in search results. It's encouraging to read about Google's architecture for automatically identifying malicious URLs. I don't think it's fair to call this Google policing the web; it's just good, ethical business to filter out the evil.

Written by Jeff Atwood

Indoor enthusiast. Co-founder of Stack Overflow and Discourse. Disclaimer: I have no idea what I'm talking about. Find me here: