They roam the web looking for web sites to sign on and list there spam. About like a tick hitching a ride on a hound dog. That way they are setting a trap so when you click on a link ( they furnished ) they get paid each time it is clicked on.
I have blocked some of there IP addresses but new ones pop up every day. About the only way to really stop them is to make the forum a pay to post item. When it comes to taking money from there pocket it really stops them in there tracks.
I heard about this one and Neil would have to install it.
There is another trick to do and that is to make the post of each new member having to have an approval , this way it can be posted but would not show on the forum till it is approved or deleted. I'm really thinking about that but it would wreck all of our fun deleting the bums as they post there junk right now.
By the way , the latest group is from the UK.
If you want to see a list of them http://www.stopforumspam.com/ipcheck/22.214.171.124