To officially be classified as 'criminal menace' (the legalese term for stalking) the person in question must harass or follow the person or people in question three or more times with malicious intent before they can be charged. Socially, of course, things are generally less lenient; just a single occasion, even without malice, even without intent, can cause someone to be labeled a stalker. But all this, of course, is provided it's in person. On the Internet, of course, there's nothing to stop it from going on indefinately.

However, I get the sense that that has absolutely nothing to do with what you're asking, and that I'm just taking the opportunity to use Wikipedia to be pretentious. I do that sometimes (read; too much). You're asking because you've posted exactly two things on here, your introduction and a call for help when the BBC Sherlock Holmes forum attacked you for suggesting...cooperation with the PPC? Something like that. Anyway, putting my not-inconsiderable research skills aside for the moment (alas), I shall spake my response thusly:

I also lurked for quite some time before I worked up the courage to introduce myself (three years, actually) and I think I understand your plight. You seem to feel that you have nothing to contribute to our dear organization, and have therefore not contributed any of what you in fact could. This viewpoint is weighing you down. You have put these shackles on, and so you can take them off yourself. When you're ready, I have no doubt that you will. However, I'm in no position to make judgements on this, and in any case, I may be full of **** with my whole theory.

The point is, I think, that you should follow your bliss, my friend. I wish you well where'ere the winds of fate shall blow you. Ciao, my dear.

board related, fic related or real life related?

My dictionary says a lurker does not participate and a stalker showers someone with obsessive and unwanted attention. A lurker to the extreme can thus not be classified as stalker, because that would mean the lurker had started taking action. Which is quite the opposite of what the lurker had been doing.