If you look at the message closely, you'll see it contains a link to a website, so their goal is probably to multiply external references to that website in order to better positioning in search engines.
It seems also an indication that the captcha used for registration is ineffective with recent spambots.
"Time is illusion. Lunchtime doubly so". Douglas N. Adams
| My mods: http://forum.spaceengine.org/viewtopic.php?f=3&t=80 | My specs: Asus x555ub - cpu i5-6200u, ram 12gb, gpu nvidia geforce 940m 2gb vram |