If you did a Google search between 6:30 a.m. PST and 7:25 a.m. PST this morning, you likely saw that the message “This site may harm your computer” accompanied each and every search result. This was clearly an error, and we are very sorry for the inconvenience caused to our users.

What happened? Very simply, human error. Google flags search results with the message “This site may harm your computer” if the site is known to install malicious software in the background or otherwise surreptitiously. We do this to protect our users against visiting sites that could harm their computers. We maintain a list of such sites through both manual and automated methods. We work with a non-profit called StopBadware.org to come up with criteria for maintaining this list, and to provide simple processes for webmasters to remove their site from the list.

We periodically update that list and released one such update to the site this morning. Unfortunately (and here’s the human error), the URL of ‘/’ was mistakenly checked in as a value to the file and ‘/’ expands to all URLs. Fortunately, our on-call site reliability team found the problem quickly and reverted the file. Since we push these updates in a staggered and rolling fashion, the errors began appearing between 6:27 a.m. and 6:40 a.m. and began disappearing between 7:10 and 7:25 a.m., so the duration of the problem for any particular user was approximately 40 minutes.

Thanks to our team for their quick work in finding this. And again, our apologies to any of you who were inconvenienced this morning, and to site owners whose pages were incorrectly labelled. We will carefully investigate this incident and put more robust file checks in place to prevent it from happening again.

Thanks for your understanding.

Update at 10:29 am PST: This post was revised as more precise information became available (changes are in bold).

This morning, an apparent glitch at Google caused nearly every [update 11:44 am] search listing to carry the “Warning! This site may harm your computer” message. Users who attempted to click through the results saw the “interstitial” warning page that mentions the possibility of badware and refers people to StopBadware.org for more information. This led to a denial of service of our website, as millions of Google users attempted to visit our site for more information. We are working now to bring the site back up. We are also awaiting word from Google about what happened to cause the false warnings.

[Update 12:31] Google has posted an update on their official blog that erroneously states that Google gets its list of URLs from us. This is not accurate. Google generates its own list of badware URLs, and no data that we generate is supposed to affect the warnings in Google’s search listings. We are attempting to work with Google to clarify their statement.

[Update 12:41] Google is working on an updated statement. Meanwhile, to clarify some false press reports, it does not appear to be the case that Google has taken down the warnings for legitimately bad sites. We have spot checked a couple known bad sites, and Google is still flagging those sites as bad. i.e., the problem appears to be corrected on their end.

For more information about how the process works and the relative role that Google and StopBadware.org play, please see our Clearinghouse page or this question in our FAQ.

[Update 1:36] Google updated its statement to reflect that StopBadware does not provide Google’s badware data.