• Physical stalking is following someone, appearing at a person’s home or place of business, making harassing phone calls, leaving written messages or objects, or vandalizing one’s property.
• Cyberstalking involves using the Internet or other electronic means to harass. A January 2009 U.S. Department of Justice report found that 23% of stalking victims suffered some form of cyberstalking, and 6% suffered electronic monitoring such as spyware, bugging or video surveillance.
  *USDOJ report "Stalking Victimization in the United States"

Either type of action may or may not be accompanied by a credible threat of serious harm. But both types can cause psychological damage, and each can potentially lead to an assault or even murder.