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 work with a non-profit called StopBadware.org to get our list of URLs. StopBadware carefully researches each consumer complaint to decide fairly whether that URL belongs on the list. Since each case needs to be individually researched, this list is maintained by humans, not algorithms.Well handled, and hopefully this does not have negative repercussions for the company long term.
We periodically receive updates to that list and received one such update to release on 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: StopBadware.org clarifies the situation a bit further, placing the blame back in Google's court:
[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.