There's actually a very simple answer for this. When you go to Yahoo.com on an iOS device it asks you if you want Yahoo to be the default search engine. Since Y

There's actually a very simple answer for this. When you go to Yahoo.com on an iOS device it asks you if you want Yahoo to be the default search engine. Since Yahoo is a popular portal (I go to Yahoo news atleast a few times a day on my iOS device) people can inadvertently switch to Yahoo. This has happened to me numerous times and I couldn't figure out why. Then I figured out that Yahoo puts up a popup which I promptly clicked "ok" to get it out of the way, then wondered time and time again why my iPhone was always ignoring my default search preferences which was Google.