Hijacker, browser hijacker, is a form of software interfering with web-browsing of the computer system concerned.  Hijacker is deemed to be a variety of adware and spyware as it also automatically plays and displays ads and may collect information on infected computer system. Browsing hijacking may be expressed through unauthorized replacement of browser home-page, search page, error page with the page hackers want users to see. Hijacker may redirect web-browser randomly or according to the predetermined schedule to the related websites and use web-browser to display messages like fake computer security warnings.