Incorrect Processing of 404 Errors
404 Page Error indicates that the server was unable to find the requested address. It means that the page has already been deleted or never existed. In this case, search engine crawlers should get 404 response — the page was not found.
But very often, this error is processed incorrectly or isn't processed at all on many websites, and the search engine crawlers get 200 or 302 responses. Using fake parameters, an attacker can create multiple URLs to nonexistent pages on your website — e.g., https://yourwebsite.com/legitimate-url?spam-fake-parameters and buy spammy links to these URLs. As these URLs return 200 response, they are treated by search engines as normal and genuine pages. So, if there are only 100 useful pages on your website, and an attacker has created 3000 useless pages, then your website can be filtered or penalized by search engines.
To protect your website from this attack, check your server response to nonexistent pages.