the push approach is more versatile and is divided into two types. a not requested service (opt-out) is the more common approach amongst the two approaches, as this allows advertisers to target users until the users do not want the ads to be sent to them. by contrast, through using the opt-in approach the users can determine what type of advertisements or promotional material they can receive from the advertisers. the advertisers must abide by certain legal regulations set in place and respect users' choices.