What is a Browser Hijacker?
When starting your browser you notice a different homepage, not the one you set it be or, when you misspell a web address you get a search engine loaded with sponsored links or ads, finally, when you enter a web address you're sure of, is right, you end up at an advertising page. These are all signs of a Browser Hijacker. Something, ranging from adware to other malware has changed your browser settings for obvious purposes.
You get a browser hijacker the same way you get other malkware, bad protection or unsafe surfing, to remove one, go here. And to prevent problems in the future go here.