I wasn't really sure where to post this, so that I can get some help. In checking the google analytics, I discover over 10,000 external links to my site. All of which, are porn spam on somebody else's forums. Of course, most of those forums are offline now. My question is this: why are they doing this? What harm does it do to my site? What can I do about it? Are they using my site as a mirror?
There is only one thing to worry about. IF your site is new, google will ban you. Other than that, an external site linking to you can not hurt you. If competitors could hurt you, think of how many people are trying to get other people's site banned.
Fireworking has it spot on I think, you can only benefit from this, unless your site is new. You might get sandboxed which can last up to 3-6 months. I've been sandboxed because one of my sites was very fresh, and I gave it plenty of links from my other ones. Some people will just try be nasty, thats the sad reality of life. But Search Engines try to protect you aswell.