kaled - 9:15 pm on May 28, 2010 (gmt 0)
If robots are able to follow the script then that is hardly cloaking. Also, even if they cannot, the url=http... format used is so obvious and common that robots may simply interpret the link to destination directly.
all outbound links are already "cloaked" (passed through a redirect script) in the forums, and have been for years.
Well, in that case, simply relax the rules in all the forums where it isn't a problem and see what happens.
See the Professional Forum Spammers thread Brett linked to above - it's happening day after day here at WebmasterWorld.
Also, I did mention the possibility of a black-list - maybe that would help.