OptimumSearch is a browser hijacker that will attempt to commandeer your homepage and redirect you to the fake search engine search.optimum.icu. Results generated by this browser hijacker will send you to malicious websites to get money from you or infect your computer further. It may also track your browsing activities, display unwanted advertisements, or prevent you from changing your settings back.
Search.optimum.icu redirects usually happen when a bundled software is installed without you knowing. In this case, it is the potentially unwanted application (PUA) OptimumSearch. You have to remove it immediately.