Any software that resets your browser's settings to point to other sites. Hijacks may reroute your info and address requests through an unseen site, capturing that info. In such hijacks, your browser may behave normally, but be slower.
Installing certain software, sometimes without your knowledge, has the unfortunate effect of "hijacking" your browser's homepage so it goes to a page other than the one you intended. Generally to a useless search engine. Often this forces all of your internet activity to pass through a third party's "proxy" which helps them to increase the amount of "hits" on their webpage thus increasing their advertising revenue. Also often used to catch personal information. Hijacking is very difficult to get rid of.
Hijack were a hip hop group from Brixton in London, featuring Kamanchi Sly, DJ Supreme, DJ Undercover, Ulysses, Agent Fritz and Agent Clueso. Their first single, "Style Wars" (Music of Life, 1988 caught the attention of the British hip hop community and laid much of the ground work for what was to come from the scene over the next few years. Their next release, "Hold No Hostage/Doomsday of Rap" (Music of Life, 1989) became an underground hit across Europe, bringing them to the attention of West Coast rapper Ice T.