Google reported Crawl Errors last week on my largest site though Webmaster Tools. Here is the message:

Google detected a significant increase in the number of URLs that return a 404 (Page Not Found) error. Investigating these errors and fixing them where appropriate ensures that Google can successfully crawl your site's pages.

The Crawl Errors list is now full of hundreds of fake links like these causing 16,519 errors so far:

Note that my site does not even have a search.html and is not related to any of the terms shown in the above image. Inspecting sources for one of those links, I can see this is not simply an isolated source but a concerted effort:

Each of the links has a few to a dozen sources all from different, seemingly unrelated sites.

It is completely baffling as to why would someone to spending effort doing this. What are they hoping to achieve? Is this an attack?

Most importantly:

Does this have a negative effect on my side? Could it negatively impact my ranking?

If so, what to do about it?

The few linking pages I looked at are full of thousands of links to tons of sites and have no contact information and do not seem like the kind of people who would simply stop if asked nicely!

According to Google Webmaster Tools, these errors have appeared in a span of 11 days. No crawl errors were being reported previously.