The car that's been been driving behind you for three blocks.

A wrong number who suddenly hangs up.

That guy who glances at you from behind his newspaper.

If you're a celebrity with a stalker, the first thing that comes to your mind every time you have these everyday encounters is: Is that my stalker? And is this the time he'll try to make good on his threats?

“It takes a while to figure out who's just a 'Deadhead,' and who's an obsessed stalker," says entertainment publicist Susan Blond, who has worked with superstars like KISS and James Brown. "Especially now with blogs and e-mail. They find out when their planes are landing, and where they’ll be next.”

But even if you know who your stalker is, keeping them at bay can be close to impossible, say experts.

"A lot of these people are sick, and its tough to control crazy," says Sunny Hostin, a former federal prosecutor and current managing director at Kroll Inc., a risk consulting company. "Without laying legal groundwork, an officer can't help you. And the only thing you can do is involve law enforcement to push the process. An order of protection and restraining order doesn't protect you from the stalker, since they are sick, but it starts the legal process."

Click here to see photos of celebrities who were stalked.

Almost a million and a half people are stalked every year, but it is the celebrity cases that make the news. Several stars have involved the legal system against alleged stalkers in recent weeks. Tom Cruise got a restraining order December 11 against an Iraq war veteran who waved a gun near a major highway before trying to deliver a letter by hand to Cruise's mansion.

Actress Alyssa Milano is seeking a restraining order against a man she says has tried repeatedly to meet her, and who, on November 16, climbed a fence outside her home in a gated community.

Jennifer Garner says a man named Steven Burky has been harassing her since 2002. When his behavior escalated in 2008, she went to court for an order of protection.

"This past year, Mr. Burky has resurfaced and his obsessive and harassing behavior has escalated to the point of becoming dangerous and threatening," she stated in documents filed November 20. "He has now shown up at my private residence and has repeatedly expressed his belief that God has sent him a vision of me being 'persecuted' in some manner that might result in my death."

But "American Idol" judge Paula Abdul's case is the most tragic. Her stalker, Paula Goodspeed, died outside of Abdul's house of an apparent suicide on November 12.

Abdul said Goodspeed, who had appeared on "Idol" as a contestant in 2005, had been stalking her for years. Abdul also said she had warned "Idol" producers that Goodspeed was her stalker before the woman's on-camera audition. (Producer Nigel Lythgoe says he doesn't remember that conversation, and "American Idol" refused to comment.)

Sunny Hostin said fueling a stalker's fantasy by granting access to the object of her obsession is a terrible mistake. “The worst thing to give a stalker is the attention they are craving,” says Hostin, “It makes the delusion a reality."

Hostin says "Idol" producers made a huge error in judgment if they knew that Goodspeed had been following Abdul.

“Giving her that audition really took it to the next level,” says Hostin, who is currently protecting a singer who wrote a song about her stalker, and is now dealing with increased activity from the stalker. “That adds gasoline to the fire. Celebrities feel compeled to respond, but the worst thing they can do is respond.”

“It wasn’t right for Paula to have to deal with that,” agrees Susan Blond who helped map out protection plans for KISS frontman Gene Simmons. “Gene gave us names of people who were particularly scary to keep out. We were told what to look for and who was seriously deranged.”