Ask HN: Service for detecting spam signups?

At our startup we've recently started seeing a surge in spam / fraudulent users signing up to abuse the service. We have a captcha on our registration form but it isn't enough.

I was wondering if there's a service out there where you can submit someones username + some other details such as name, email etc and it would give a rating on how likely that signup is to be a spammer or a legitimate user.

Does something like this exist?

It's fairly easy as a human to look at a new users details and determine whether they are likely to be a spammer or not (random character username / email / names or a bunch of accounts signed up in quick succession with similar details) but we don't have the resources to do this and it would be great to have an automated way to do this.