I've had a client that had one of their sites dropped down past page 300 on Google for their main search term. It turned out that somebody had sites banned by Google linking to their site with the key words that they are going after. The company had to take legal action on the sites to get the links removed.

Is there any on-line tools or software that can be run to determine if somebody is using Negative SEO to either bring down your web site or push you down on your key words?

When doing a Google search for sites linking to you, Google only shows sites with a somewhat high page rank. Since a banned site will have a gray bar for the PR, these sites will not show up as one of the back-links. By checking Yahoo or Alta Vista back links, how else can you easily find out Google banned sites that are linking to you without having to go through each site, one at a time by hand to check the Google Tool Bar? Is there any fast, automated way of finding this out?

I would appreciate any feedback on this as I am sure there are a lot of concerned webmasters regarding this issue.