The process of collecting as much information as possible about potential clients and customers from information they have entered into forms on various web sites is called

spying
personal intrusion
data mining
data exploitation

The correct answer would be Option D, Data Exploitation.

Explanation:

Data Exploitation is to use someone else data to ones own advantage. As the name suggests, data exploitation is to exploit the data of someone. For example in this question, it is said that when people enter their details on various sites and give information about them to certain sites and other people use such information of them to have possible advantage from them, and to make them their clients, then such process of collecting information without their permission is called the data exploitation.