Hi Min
The problem is these people will be based overseas and are virtually untraceable. They may not even be selling anything, just luring people onto a website loaded with viruses or trying to get details for identity theft.
The individuals doing this won't even be aware of who we are. They will have some system that scans the web for forums, they log in, copy and paste their message and move on to the next forum. One of the joys of being connected to the world!
I've set up a system that monitors our forum for certain words and sends me an email when suspected spam is posted. It's not fool proof but it should at least help me keep an eye on things.
Cheers
Stuart