Google wrote, “On Monday we detected an issue with our indexing systems that affected Google search results. Once the issue was identified, it was promptly fixed by our Site Reliability Engineers and by now it has been mitigated.”
The confirmation. Here is the tweet confirming the issue and the explanation:
More information. You can learn more about this issue and the impact on sites in our story from this morning.
Postscript. Many, including myself, were not too happy with the short explanation from Google. Gary Illyes from Google tweeted additional information about why the indexing system is vital to how search results show up:
Google Caffeine launched in 2010. Learn more about Google Caffeine here.