I recently had a very concerned lady call me about her website, and how she thought someone was “interfering” with her site by adding links to her site from other “bad” and “spammy” sites.
Well, the answer is: you cannot control who links to you, nor how they link to you.
This might sound like a horrible situation, but its just the way it is.
A real-world comparison is: can you stop someone from sending you letters via the post?
Of course the answer is: No
If someone wants to wast their money sending you hundreds of letters per day, then there is little you can do… Particularly if they send the letters from different mailboxes…
But its not as bad as it might seem.
Google (and other search engines), keep track of the “neighbourhood” that your site belongs to. This means: if you have a music web site, and most links from your site point at other music sites, and other music sites have links pointing to your site… then google will put your site into its internal “music” category.
So, if your site gets some links from, say, a computer website, or a “spam” website, then google will automatically “tone down” the importance of those unrelated links.
What you should never, never do, is link back to the unrelated websites, out of “revenge”. This will tell google that you want to take part in the category of the unrelated website (by effectively “voting” for it)… this will make the “bad” links more important, and seriously downgrade your site “in googles eyes”.
So, the best way to minimise the effect of bad links to your website is to make sure you have good links to your website.