"When I open Chrome, the home page is automatically redirects to https://nz.search.yahoo.com/?type=994519&fr=yo-yhp-ch. And if I go into Settings, I find that the Search engine from the Omnibox is also set to Yahoo..."
Know more about "https://nz.search.yahoo.com/?type=994519&fr=yo-yhp-ch"
"https://nz.search.yahoo.com/?type=994519&fr=yo-yhp-ch" is a fake yahoo search that can be regarded as a kind of browser hijacker. Accoring to most cases, it is capable of modifying your browser default settings including homepage and search engine. Nasty as it is, you are blocked to visit other certain websites. It is really urgent to remove this fake yahoo search.