Google AdWords claiming my site has an "existing compromise that prevents referrer URLs from successfully visiting the site through an ad"

Question

Here's the email I just received from Google about why they won't turn on my AdWords account after my hosting provider had DNS issues which caused AdWords to believe the site was compromised by malware:

The destination URL: http://www.mysite.com/page is returning a 404 error when our systems scan it via an ad click. This indicates that the site's server likely has an existing compromise that prevents referer URLs from successfully visiting the site through an ad. Please note that the URL may still work when directly visited in a browser since the referer URL is a completely different setting.

Is this actually possible? There's no other way to reach the page other than using the URL to it. I thought a referrer URL is in the header of the HTTP request, and simply stored the URL of the page you were just at.

Are they saying that there's some kind of malware on my site that's filtering requests based on the value of the referrer URL? Have any of your ever had this problem?

Answer 1

Are they saying that there's some kind of malware on my site that's filtering requests based on the value of the referrer URL? Have any of your ever had this problem?

That type of malware is very common on websites these days. It usually happens when when an attacker is able to access the website files (possibly through a sniffed or guessed FTP password.) It is very common for the attacker to alter an htaccess file where they can add rewrite rules based on referrer.

Google has put together a very comprehensive guide to dealing with malware on your website. It looks like Google has contacted you through AdWords about this issue, but they may also provide additional information through Google Webmaster Tools.