XRumer is a Windows program that posts forum spam and the aim of the product is to boost search engine rankings. It has been claimed that the program is able to bypass techniques commonly used by many websites to deter automated spam, such as account registration, CAPTCHAs, and e-mail activation before posting. The program makes heavy use of a database of known open proxies in an attempt to make it more difficult for administrators to block posts.
On a side note, it's a bit expensive, it's buggy and as I remember - in Russian.