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I think it's likely that the web is being continuously flooded by millions of these spammy links created by automated methods, often by scraping Google's own SERPs from random keyword searches. But the pages they are on appear to be ephemeral, and disappear after a short time.
I thought of this too, but you are saying that if someone like a competitor scapes Google's own serp's via random keywords by some automated software, they now can take you down and damage your rankings and reputation by using spammy links pointed to your website.
Because its unclear where these links may have come from these links should be just discredited or devalued and not hurt or penalize the website that unknowingly received them.
ALL my links all at the same time on Google drop on average 60 positions
Is there a glitche with the Google webmaster tool?
I have checked around on google groups and other google forums and there appears to be an epidemic of webmasters claiming inflated reporting using the WMT link report.