The browser hijackers aren’t dangerous like Ransomware, Spyware, or other threats. The whole purpose of these unwanted applications is the online promotion of different sites, services, web stores, and so on. However, in order to be effective at their job, most hijackers resort to some rather aggressive advertising techniques. Take for example the ads they display - most of them would be placed over the parts of the web page that are likely to be of most interest to you. If you are reading an article or watching a video, the ad would probably obscure them, thus forcing you to click on it to get it out of the way. Of course, this will solve nothing in the long term as the ads will keep on coming to obstruct you. Also, in some cases, you could get directly redirected to a given site without clicking on anything or the redirect links would appear over the buttons on a page so instead of clicking on the given button, you would be interacting with a link that will land you on some other sites. These, and other similar sneaky tactics employed by apps like Flowdeal are one of the main reasons why the browser hijackers are seen as unwanted.