They've shown up in Selena Gomez's guest house, outside Halle Berry's kitchen door and inside Sandra Bullock's home, despite gates, tall fences and guards meant to keep the stars safe.
Celebrity stalkers continue to be one of stardom's most troubling downsides. Many instances involve serious cases of mental illness, making it difficult for private security, police and prosecutors to anticipate those intent on harassing and possibly harming some of the entertainment industry's biggest names.
Yet today's celebrities have greater protections from stalkers due in large part to the murder 25 years ago of actress-model Rebecca Schaeffer.
At 21-years-old, Schaeffer was shot to death at the door of her Los Angeles apartment on July 19, 1989, by obsessed fan Robert Bardo. The Arizona native, who had written Schaeffer letters and tried to meet her at a studio where she worked, tracked the "My Sister Sam" actress down after paying a private investigator to obtain her home address from state motor vehicle records.
Bardo remains in prison, serving a life sentence without possibility of parole.
The legacy of Schaeffer's death is evident multiple times a year in Los Angeles courtrooms when celebrities such as Madonna, Steven Spielberg, Ryan Seacrest, Paris Hilton and others become stalking victims.
Protections created after Schaeffer's death include laws that make stalking a crime, restrictions on public access to address information from driving records in California, and a specialized Los Angeles police unit that works with prosecutors, celebrity attorneys and security details to keep obsessed fans a safe distance away.
Criminal penalties for stalking have also been adopted in other states.
The protections don't eliminate the various ways celebrity stalkers can torment their victims, from unsolicited love letters to threatening tweets, break-ins and kidnapping plots. But they can eventually put a stop to the threats.
Stalkers can make celebrities "a prisoner," said Los Angeles Deputy District Attorney Wendy Segall, who has prosecuted celebrity stalking cases for the past six years. "They never know when this person is going to show up."
Many of Segall's cases end with stalking convictions and sentences that require the defendant to get psychological counseling. The sentences, Segall said, allow stalking victims to again feel safer.
Men who stalked Gomez and Berry have been convicted and ordered to undergo psychological counseling. Joshua Corbett, who was arrested last month after breaking in to Bullock's home, has pleaded not guilty and remains in a Los Angeles jail. A search of Corbett's home turned up an arsenal of illegal firearms, including machine guns, although he did not have any weapons at the time of his arrest.
In felony stalking cases, victims can obtain a 10-year restraining order -- far longer than the three-year stay-away order that can be obtained from a civil judge.
"Arrest and conviction is only one part. It's not a solution. We recognize that intervention is really what we're going for," said Chuck Tobin, the president of the Association of Threat Assessment Professionals, a 1,200 member organization of law enforcement and private security officers who protect celebrities, politicians and other dignitaries.
Tobin said the Los Angeles Police Department's Threat Management Unit has been a leader in the field. Detectives in the unit routinely testify against suspected stalkers in criminal and civil courts, and are increasingly searching social media and online sites for evidence of stalking.
Retired Los Angeles Police Detective Paul Coulter's first homicide case was investigating Schaeffer's death and retracing her killer's steps.
Coulter said authorities knew of the problem with the release of driving records before Schaeffer's death, because an obsessed fan had stabbed and seriously injured actress Theresa Saldana years earlier. Yet it wasn't until Schaeffer's death that policies changed.
He said it was up to policymakers to determine if more changes are needed now, with celebrity access, including home addresses, increasingly available online. The veteran detective is fairly certain however that no matter what deterrents are in place, some people will continue to develop unhealthy obsessions with the famous.
"I don't think it's ever going to change," Coulter said. "You're always going to have people fascinated with the celebrities."
The Internet may have made sending messages to celebrities easier, but stars have long had to contend with unsavory contact, including a 1949 case in which three obscene letters were sent to Elizabeth Taylor, then 17. Despite painstaking comparisons with other threatening letters, no suspect was ever identified, according to FBI files, although in 1952 a man was arrested on suspicion of harassing Taylor and falsely identifying himself as an FBI agent.
In the 21st century, stalkers' use of the Internet for harassing stars can leave digital fingerprints used by authorities and private security investigators to track suspects and strengthen cases against them.
Coulter said just as laws improved celebrity safety after Schaeffer's death, stars will learn how to use social media without putting themselves in danger. "It's just a new problem that they have to deal with," he said.