stalker

Stalking is unwanted or obsessive attention by an individual or group towards another person. Stalking behaviors are related to harassment and intimidation and may include following the victim in person or monitoring them. The term stalking is used with some differing definitions in psychiatry and psychology, as well as in some legal jurisdictions as a term for a criminal offense.
According to a 2002 report by the U.S. National Center for Victims of Crime, "virtually any unwanted contact between two people that directly or indirectly communicates a threat or places the victim in fear can be considered stalking", although in practice the legal standard is usually somewhat more strict.

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