Well i agree that anti virus software is the ultimate solution. If it is not updated regularly our system may be in risk...
In fact i think we neednt have to intentionally visit any porn site..sometime the keywords we search makes us to view some links of porn site or content...which is unavoidable and accidently we may even click them.
Game sites are also risky and people who play games of different types must have searched for cracks onlne...where the sites providing this cracks defientely have some viruses or other risking programs...
