Spammer making external links to competition 404 page

If the bad links come from spam pages, then I'd just let them stay 404. There's no reason to tell Google that you want to be associated with those sites.

A high number of internal links that are 404 is a negative quality signal - but not external links from sites that are outside your control.

It doesn't show me where they are coming from, they are under
Diagnostics / Crawl errors But these links are not on our site like that anywhere.

They almost look as if they are forum post links the way they are shortened, but then maybe someone scraped the forum and only took the text of the link and not the full url code if that makes sense.

It doesn't show me where they are coming from

This may be exactly what you mean, but for clarity's sake I've got to ask. Do you mean the column under "Linked from" (over to the right) is completely blank?

Can we do a short survey in this (or maybe other) thread to figure out if sites with lots of example.com/widg... 404 errors are de-ranked? I have hundreds of 404s these and the site was de-ranked heavily after Panda.

We have hundreds of ... links as well in WMT, and hit by Panda, but I don't relate the two events.

Still it's a bit odd WMT doesn't show where they come from, perhaps originating site(s) have been removed from SERPS

I've got scores of sites I check in on regularly - some were hit with ranking losses around the time that such bogus backlinks showed up, and others were not deranked at all. So I agree with johnhh, there doesn't seem to be a connection.

One site I know of tried a reconsideration request and spelled out all the bad links. The result was a "no manual spam penalty" message.

Dynamic pages - these might be a problem. If a competitor sniffs out a dynamic page and can make it show empty pages then links to your empty pages reflect badly on you. I think Matt Cutts has a personal vendetta against poorly executed dynamic pages too and I'm 100% positive googlebot can test random pages when it suspects a dynamic url, and maybe even when it doesn't.

google is in the biz of recording everything, I think it's quite capable of finding this type of problem :)

If the bad links come from spam pages, then I'd just let them stay 404. There's no reason to tell Google that you want to be associated with those sites.

I suspect but can't prove that leaving the spam 404 pages in the google WMT means that google is in effect indexing these non-existent pages to my website. This is why I think it effects overall rank of the site. Let me put it another way. This type of attack is wide spread. You can read about it happening to many sites around the web. Why would anyone spend the time and resources to do it unless it had a negative effect on the site being hit with the spam links? One of my sites has received over 500 of these spam links in the last six months. The origination of the spam links are spread over hundreds of URLs.

I hope Google doesn't consider these spam 404 pages as thin content.

Regardless of how google is handling it, there is no reason why the WEB should be broken! 404 means just that: Page Not Found. I, too, would like to be proactive, but there's no way to deal with malice of this type and there are other things to do (besides sucking down a gallon of Pepto every day!)

I have to admit that these links are annoying and might put a bad light on a site. [Although I ignore these links and continue to ignore].
WMT Google Employees must know that these links are spammy ones and should be treated as such.
I hope that they have red this thread.
Tedser,
can you bring this discussion to their attention? we know of Pier for example.