If your browser search and default homepage directs to Search90.com, then you’re most probably infected with a browser hijacker.
The browser hijacker will load lots of undesired advertisements whenever you do a custom search. The developers simply generate advertising revenues through these intrusive pop-up or in-text ads. Search90.com tries to mimic actual search engines like Google, Yahoo or Bing in order to send you to malicious websites to get money from you or infect your computer further. It may also prevent you from changing your settings back.
Search90.com is usually installed through bundled software without you knowing. Remove it immediately.