I want to know more about spam on forum

when i surf inet and forum like this I often see message like this:

Let me know if you see my link here?

morgage loans
loans[/url]
loans[/link]


homeloans




refinancing mortage
mortage[/url]
mortage[/link]


freeporno




cialiss




buy viahra
viahra[/url]
viahra[/link]


tramdol




buy viafra
viafra[/url]
viafra[/link]


cialiss/a>




If I do something wrong please let me know! -----

why people do this