Does anyone else experience this problem with unwanted backlinks?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Neil Cassels: Does anyone else experience this problem with unwanted backlinks, if so how have you dealt with it?
  One of my sites has a bunch of links like these, mostly pointing to non-existent member pages. The links mainly seem to come from Polish language forums and the posts are obvious spam.
• 
  Jim Munro: I am not an expert, Neil, but I've heard John Mueller talk about this.
  
  If the landing page is 404 there is nothing to be concerned about but if there is a landing page you can adding the referring domain to your disavow file and forget about them.
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  Jim Munro: For +Tim Capper ;I should add that apparently Google intends to create a tool to process the disavow file. :)
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  nathan Graybill: how are you getting those links? im wondering how it happened. spammy link building tools or something?
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  Neil Cassels: +nathan Graybill ;I honestly have no idea. I haven't used link building tools, or paid for backlinks. ;
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  Neil Cassels: +Jim Munro ;thanks, mostly they are to pages which don't exist. either member pages, or some weird extension to member pages which appear to be attempts to access some sort of exploit.
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  ?ukasz Rogala: I can tell you why and how we get those links. ;)
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  Neil Cassels: +Łukasz Rogala ;Please do :)
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  Borislav Arapchev: Maybe - negative SEO ; - competitor buy 1000 low quality ; links to your site for 10 usd and hurts you. Use disavow tool.
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  ?ukasz Rogala: So basicly it is just about automatic link building. We don't do this manually. You need to hate Xrumer developers for making such a cool software which is able to get that kind of links (also you need to hate Scrapebox for auto commenting and profile making). :P
  It is cheap, works fine and provides rankings for the main site.
  
  Probably your site gives an option to place a "dofollow" link, so that we can use it for ranking issues. But it is not about the link making ofc - you need to link place which is linking to your site. So that you get some kind of pyramid of links in order to get more power of each link, and that is why you get so many polish anchor texts.
  
  If you want to prevent from those kind of links simply make "noindex, nofollow" on each member page. Also check for IPs of each account and ban any multiaccounts they make. You can also fight with IP blocking of each Xrumer service, there are special forum which provides information about spamming IPs.
  
  Btw - drop link to your site here, I will remove it from my links lists if I will find it. :P
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  Joseph Paulino: +Neil Cassels ;I think what you have there is referral spam. Matt Cutts says in a recent video that these things can't possibly harm your rankings because Google is doing a good job of preventing anybody from doing  ;harm against anybody. He says you can disavow them if they worry you a lot.
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  Jim Munro: Hi +Joseph Paulino ;. I'm not sure but I think I might listen to +Łukasz Rogala ;before I'd listen to Matt Cutts; :)
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  Neil Cassels: +Łukasz Rogala ;ahhh yeah that totally fits. I guess these got going before the site was completely finished and 'hardened' hence the non-existent member page. Great info, thanks ;)
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  Neil Cassels: +Joseph Paulino ;thanks - I think +Jim Munro ;is right though, I don't have complete confidence that this sort of thing is harmless and the safest thing to do is disavow.