You may do everything on your part to make sure to avoid such risky websites and even downloads, but then one day you make the mistake of allowing a close friend or even family to use your device for something they claim is important, and then they visit a risky website or make a download they think is harmless. All your effort at security goes to waste. It is necessary to try as much as you can to make sure that you are the only one using any device where you have important and sensitive information and application. Other people around you may not mean you harm but you can be the only one as careful with your device as you would want.