What's the best service to use for filtering out spam/abuse/malware links for a link shortening webapp?

I have two services - Lincr and LinkBunch. Lincr is a plain jane URL shortening service, while LinkBunch lets you shorten multiple links into one link. I've had too much spam posted into the services, so I had to shut down Lincr. Now, even LinkBunch seems to be facing the same problem, and it's been disabled by my web host for that reason.

I can't keep shutting down sites like this because of bad links being posted, so I need a malware-filtering API that I can use to f开发者_StackOverflowilter out the links as and when they are posted.

There are services that let me download an entire bunch of bad links to check against, but instead, I'd prefer doing a live API call on a per-link basis. What can I use for that?

Finally, what's the best malware filtering service out there?

Lincr is down. On LinkBunch, where is your Captcha?

On either site, do you limit the number of posts by IP? Do you use a delay in your response? What about using hidden fields to reduce spam (http://www.reviewmylife.co.uk/blog/2008/05/30/hidden-field-spam-trap-for-phpformmail/)?

I know I'm dodging the question a bit, but you should at least take basic anti-spam measures before resorting to API calls. Even APIs will still fail for newly-hacked / newly-spammed sites.