Celebrity stalking is not unheard of. In fact, the number of celebrities requesting for restraining orders against stalkers have increased, since let's say, John Lennon's time - when he was killed by Mark Chapman, an obsessed fan.

But what is celebrity stalking really? An obsession? A mental illness? A crime? Here is what experts say.

Delusional stalkers

Celebrity stalking falls under the category of delusional stalking where the stalker usually has very little or no contact at all with the victim.

The stalker usually suffers from mental illnesses such as manic-depression, schizophrenia and erotomania. Wikipedia defines erotomania as a rare disorder where the subject holds a delusional belief that another person, usually of higher social status, is in love with him/her.

Erotomaniacs actually believe that the person they are stalking, in the case the celebrity, is having a relationship with him/her. An example of this is David Letterman's stalker Margaret Ray.

A common denominator of delusional stalkers is the false belief that keeps them bound to their victims.

Another form of delusional stalker believes that the intended victim is his/her destiny. They know that they are not having a relationship with the intended victim, but they believe that if they pursue the celebrity hard enough, the said celebrity will come to love the stalker.

Profile of a delusional stalker

A typical delusional stalker is a loner who is socially immature and thus unable to start or keep close relationships, rarely goes out on dates and has little or no sexual relationships. They at the same time yearn for and are threatened by close relationships which could explain why they choose victims that are "unattainable".

In other words, delusional stalkers get the love and closeness that they cannot get in reality through fantasy, making it hard for them to let go.

The background of a typical delusional stalker background is either abusive or lacks the loving and caring atmosphere of a normal family. He/she has a poor sense of self-identity when growing up. They are also inclined to suffer from mental illnesses.

All of these leads them to search for satisfaction through other people, usually of higher status.

How long does a "stalking" last?

These delusions can last for quite a long period of time. Studies claim delusional stalkers to be the most tenacious of all types of stalkers.

It has been reported that erotomania can last an average of ten years - a considerable length of time considering that the stalker has very little or no contact at all with the victim. Experts believe that this is where the victim should do his/her part.

Experts say that a victim of a delusional stalker should say "no" only once. It is imperative that they don't respond to the stalker again because it will only keep him/her coming back for more.

The delusional stalker is also able to explain the victim's "no" away, thinking that "he/she loves me but the spouse or manager told him/her to say 'no' or get a restraining order."

Delusional stalkers are also usually unemployed or underemployed which means they have time in their hands. Delusional stalkers are usually smart and think their moves through and are obsessed with trying to communicate (through any means) with their victim.