A WebmasterWorld thread has a story of a webmaster who received a phone call from someone with an Indian accent threatening to use negative SEO on their site if they don't pay up. A form of search pirates, if you will.
This is what the webmaster's client said:
So I had a client phone me today and say he had a call from a guy with an Indian accent who told him that he will destroy his website rankings if he doesn't pay him £10 per month to NOT do this. What the hell...
What can you do? Well, you can monitor your new links in Google Webmaster Tools and anything that looks bad, add them to your disavow link file. It shouldn't cost or take too much time to do that.
Of course, Google has said time and time again that while negative SEO is hard it is possible.
Which is why they came out with the disavow link tool.
So track your new links in Google Webmaster Tools and disavow the bad new links.
Forum discussion at WebmasterWorld.