The verification words (CAPTCHAs) are fairly easily beatable these days – certainly those used by most forums.
You could look into replacing it with a harder one, or at least a non-standard one. Spam is a numbers game – the spammers develop automated tools to beat the standard verification methods used on the majority of sites. If your site uses something different, it will not be automatically spammable, and no-one will bother to spam it.