<p>I am trying to get data from my server, used RemoteObject to accomplish it.
When I run the application on my localhost it works great but when iam using it on my server i get a Channel.Security.Error(Security Error accessing URL).</p>

<p>On the server side logs there is a mention about cross domain .
77.127.194.4 - - [23/Oct/2008 21:15:11] "GET /crossdomain.xml HTTP/1.1" 501</p>

<p>Any one encountered the same problem ? any idea ?</p>

One thing you didn't list, that are used commonly to detect bad crawlers.
Hit speed, good web crawlers will break their hits up so they don't deluge a site with requests.  Bad ones will do one of three things:
hit sequential links one after the other
hit sequential links in some paralell sequence (2 or more at a time.)
hit sequential links at a fixed interval
Also, some offline browsing programs will slurp up a number of pages, I'm not sure what kind of threshold you'd want to use, to start blocking by IP address.
This method will also catch mirroring programs like fmirror or wget.
If the bot randomizes the time interval, you could check to see if the links are traversed in a sequential or depth-first manner, or you can see if the bot is traversing a huge amount of text (as in words to read) in a too-short period of time.  Some sites limit the number of requests per hour, also.
Actually, I heard an idea somewhere, I don't remember where, that if a user gets too much data, in terms of kilobytes, they can be presented with a captcha asking them to prove they aren't a bot.  I've never seen that implemented though.
Update on Hiding Links
As far as hiding links goes, you can put a div under another, with CSS (placing it first in the draw order) and possibly setting the z-order.  A bot could not ignore that, without parsing all your javascript to see if it is a menu.  To some extent, links inside invisible DIV elements also can't be ignored without the bot parsing all the javascript.
Taking that idea to completion, uncalled javascript which could potentially show the hidden elements would possilby fool a subset of javascript parsing bots.  And, it is not a lot of work to implement.