Poor Microsoft - 2015 hasn't been too kind to it so far. We reported just yesterday that Google exposed a rather big Windows bug to the world simply because Microsoft didn't patch it in time, and now, we learn that a bad code update conducted yesterday knocked out the company's Bing search. That in turn took out Yahoo's search, as it's based on Bing.
Another service that was temporarily affected by the outage included Apple's Siri personal assistant.
A bad code update can result in various levels of problems, but for Microsoft, the biggest problem was merely rolling the update back. For a company like Microsoft, that's unusual, as setups are (and should be) designed to allow staff to revert the changes on-the-fly. However, as with technology problems in general, sometimes things "just happen" that weren't anticipated, and it goes without saying that Microsoft's search setup is going to be more complex than most.
Ultimately, the search seemed to be down for just a couple of hours, but that was long enough to create a huge backlog of search queries for Yahoo - once the fix was in place, its servers had some serious work to do. Either way, it's quite the thing to happen mere months after Yahoo joined forces with Mozilla to deliver search in Firefox.