Someone recently started up a spam site using a domain name similar to one of mine. I don't know what advertising they're running but people are searching for the name of their site on Google. The problem: my site is ranked number one for the name of their site since it's so similar to mine. The result: a huge influx of visitors to my site I'm not complaining. I think it's fantastic. But, a helpful hint for marketers, consider what your potential visitors would search for if you tell them about your site. Chances are people are not going to click on any links in a spam e-mail they get but they make look up the company on Google. The number one hit is probably going to get the most clicks from there so make sure your site is number one on Google for your company name. If it's not, you're paying for people to go to the site that is.
I would love to have your problem... I really recommend do NOTHING!!! let them keep the hard work and you the benefits!! Cheers