IStock Photo 2716390 © Ferran Traite Soler

ESPN reporter Erin Andrews had no clue someone was calling the hotels she stayed in on assignment, pinpointing her arrival date and then attempting—sometimes successfully—to book the adjoining room. She had no knowledge that the door peepholes were being tampered with, enabling her stalker to not only watch her, but to film her using his cell phone. Andrews had no idea—until pictures of her, undressed, suddenly appeared all over the Internet.

For celebrities and others engaged in highly visible pursuits, attracting a stalker almost seems like it comes with the job. A stalker was arrested outside the home of Audrina Patridge, star of The Hills, in mid-February. Three months earlier, an Army Reserve sergeant obsessed with Ryan Seacrest entered the E! offices armed with a knife; he was on probation from an earlier assault on one of Seacrest’s bodyguards. A stalker repeatedly sent notes and flowers to Tyra Banks, threatening to slit the throat of her assistant. And 16-year-old Olympic gymnast Shawn Johnson was terrified when a stalker jumped a studio fence and tried to find her on the set of Dancing with the Stars. A search of his car uncovered loaded guns, duct tape, and love letters.

The list of well-known victims is almost endless, from Michael Douglas to Uma Thurman to Richard Gere to Sandra Bullock. But anyone can become a victim, and the motivations of stalkers vary widely. The odds a stalker is a former lover are 1 in 7.63, but they can also be neighbors or friends (1 in 6.1), or total strangers (1 in 10.31). And sometimes stalkers seek out multiple victims. According to the lawyer for Erin Andrews, her stalker videotaped at least 16 other women, including one who has been left so terrified she barricades her bedroom door every night.

Stalking—any unwanted, repeated, or continuing contact that causes a person to feel threatened, harassed or intimidated—is all too common. The odds an adult will be stalked in a year are 1 in 71.94; singling out adult women, the odds are far higher—1 in 50. And according to a 2009 Justice Department study, only one in three cases of stalking is ever reported.

Certain groups of people are more likely to become victims. The age group most at risk is 18-19 year olds; their odds of being stalked are 1 in 33.67, and those 20-24 face odds almost as high (1 in 35.21). People 65 and over are the least likely to be stalked (1 in 277.8).

Cell phone technology and the Internet have given stalkers more weapons and more reach. Today, the two most common forms of stalking are unwanted phone calls and messages (1 in 1.51—66%) and spreading rumors (1 in 2.8), often via the Internet.

In November, 2009, Vernon E. Miller was convicted of making nearly 4,000 calls to his former girlfriend in a single month. In February, 2010, Devar Hurd was sentenced to two years in jail for texting sexually explicit messages about Grammy Award-winning singer Ashanti to her mother. The messages included pictures of his genitals and pictures snapped outside her home.

Victims often report they believe the stalking began as an attempt to retaliate against a perceived wrong, or out of spite, or from a desire to gain control. Whatever the motivation, a certain percentage of stalkers will back off when confronted with police action, a fact which has encouraged celebrities like Justin Timberlake to seek restraining orders against disturbed and potentially violent fans. Of course, restraining orders don’t always work. On February 26, 2010, a stalker named Jed Waits murdered teacher Jennifer Paulson. A protective order against Waits had been in effect for more than a year.