I noticed that AwStats for my most popular blog is reporting a large number of links from various subdomain pages within a couple of porn sites. When I visit those pages, there are no links to any other sites.

I suspect the porn site may be using cloaking and substituting my content for search engines or is up to some other black hat mischief. I checked a number of the porn site's cached pages in Google and don't see anything unusual, but something strange is happening.

Does anyone know what is going on here?

What can I do to stop this?