Spammers

Our Elgg 1.5 site, UnionBook, is being hit by a massive wave of spammers who are successfully registering and validating their accounts despite the fact that we've enabled the site access plugin which has a kind of numberic captcha built in.

I've just added a site-wide password in the hope that spambots won't read it, but we need a long-term solution -- what works best in Elgg to prevent these scumbags from signing up to our sites?

Thanks.

Eric Lee