Barry Schwartz at SERoundtable noticed a huge increase in the number of websites that were showing hacked warnings in the Google search results yesterday. Most of the webmasters who posted on the Google help forums couldn’t find any evidence that their sites had been hacked and there were no notices showing up in Google Webmaster Tools, but Google was still displaying an alert in the search results that the site was hacked.

It turns out that the issue was a new hacked page classifier that Google is slowly rolling out. John Mueller shared on Google plus that there are some webmasters to run into problems and they are working to address them.

We’re slowly rolling out a new hacked page classifier and noticed a small number of misclassifications. We’re sorry for any trouble this may have caused — we are working on addressing the issues.

He doesn’t specify exactly what has been changed, but hopefully it is something to provide more guidance, especially to newer webmasters on how their sites were hacked and what to look for.  With spammers getting stealthier about how they hack sites and hide the footprints from webmasters, some do find it difficult to find the hack and then fix it.

Mueller also recommends that if you are one of the sites that has been improperly flagged that you submit a feedback form if you are certain that your site is not hacked.

As Barry noted, many of the sites that received warnings were adult sites, so there could’ve been some sort of flagged it was tripping or a resource on the site that many adult sites use that is causing the sites to be flagged as hacked.

It ironically came right after Google Webmaster Central Blog did some case studies on hacked sites to help webmasters through the process of cleaning up a hacked site.