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Hi Matt, Google probably will ignore all of these - they are pretty good at recognising spam like this, but to err on the side of caution, start to disavow the spam sites as Nick said. It's fairly easy to do if you haven't done it before, but I know you can build a disavow file from within Ahrefs. -Andy

If they are external links, and they are pointing to URLs that no longer exist, I wouldn't worry too much about it - it's unlikely that something that is so clearly spam is going to affect your site in any way. If you are really concerned about it, you could disavow the linking sites in Search Console. I hope that helps. I'm still a little unclear as to what you mean by repopulating your back end in this context.