You've been infected by some malicious hijackers. Browser hijacker is a computer threat designed to alter your web browser's settings and redirect you to the unsolicited website. Its main malicious purpose is to get extra profit. Here is a blog telling about the hijackers and other useful info. Hope this makes sense.

This may be a malicious toolbar. Malicious toolbars are often bundled with other kinds of parasites. So it can not only take up high resources and strikingly slow down your computer, but also bring you dangerous infections. Can't get rid of it yourself? You can ask help from Tee Support online removal support. Good luck!