Cactus Search is advertised as a browser extension dedicated to helping rare plants. It claims that they use their ad revenue to help plants from becoming extinct. While it may look like an ordinary search engine, Cactus Search is actually a browser hijacker that will attempt to commandeer your browser search and homepage. Generated search results will send you to malicious websites to get money from you or infect your computer further. It may also fill your screen with ads and prevent you from changing your settings back.
Cactus Search is usually installed through bundled software without you knowing. Remove it immediately.