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My gut reaction is the same as Marie's - it doesn't sound like a typical negative SEO approach. It seems more likely that a past SEO attempt by a 3rd party went farther then you thought or got spread/duplicated somehow. Unfortunately, there's virtually no way to tell who created a link (let alone why). If many of these are coming from just a few domains, I'd also recommend using the disavow tool. I do agree with James that these links could potentially harm you, even no-followed. I'd look for any common clues as to who might be leaving these comments, though. I'd just want to make absolutely sure it's not someone operating on your behalf. I've seen that way too many times in the past.