Leosghost - 11:09 am on Oct 23, 2011 (gmt 0)
External links have always been able to hurt a site, "blackhats" have been selling the "bring a site down" "service" for many years now, using software designed to generate large /massive numbers of links ..and adding human placed links has been used in conjunction with that, to refine the technique, or "sharpen the point of the knife" used to wound the target site.
Nothing new here, an old technique..in this respect Google has always been "broken"..despite Googles claims in the past..
Google have assured us of many things , a lot of what they say, needs to be treated with suspicion and more than a grain of salt ..( they changed their wording on this matter a long time ago from "nothing" to "almost nothing" incoming links from a competitor can do to harm your site*.
If this technique could not work , neither could "Google bowling"..they depend on very similar quirks of the algos..
As g1smd says..strictly speaking it may well be a matter for the police ( but that depends on what is covered by the laws in your jurisdiction ) ..even if these threats do break a particular law in your jurisdiction, you may well have to trust to "blind luck" to get your complaint as far as someone who actually understands how the web and Google's algos in particular can be manipulated..
IMO you should also contact Google urgently, giving them all the details, they may decide to "ignore" these links when rating you, the fact that they have been able in the past to take manual action to nullify certain famous cases of "Google bowling" demonstrates that they can do so ..whether they will in your case, is another matter..
But you won't know if they will act, unless you try to contact them..
*paraphrasing.. as I can't find my copy of the original text from Google,( before they changed it )..it is on an archive HD, which is hard to get at right now..