It is not Spanish but English, but it is used in our language with the same meaning of "persecutor, harasser, who lurks", almost always with a person as a victim, who is often watched without knowing it. Also 'Stalker' ( 1057; 1090; 1072; 1083; 1082; 1077; 1088; , Andrei Tarkovsky , 1979 ) is the name of a Russian science fiction film.
This word is not actually a word of Spanish but English origin. If I decide to comment it is because in other languages such as Italian, yes it is used with some frequency, along with others of the same family and root. a " 34 stalker; It is almost always someone who harasses another person. The reasons may be different, being the meaning of " 34 sexual harasser; the most usual. Sometimes the field expands to other situations in which the harasser does not persecution for sexual reasons and itself as a form of supervision or control, which can be more or less discrete and that includes, for example, computer spy or which quietly keeps track of an animal that seeks to hunt.