FIRST, IF YOU want to skip my less-than-eloquent explanation of the problem see these page on webmaster sites: kuro5hin and layman's guide.
In following links to index the web Google routinely asks servers for pages. Servers return a brief reply of the page's status. The well known 404 means that the page wasn't found. Other server responses are ones like the 200 which means "OK". Lesser found responses are the 301 (permanently moved) and the 302 (redirected/moved). The 302 is where the problem lies. I'll come back to that in a second. (Server header references: Official site | A better and clearer explanation about server headers).

Most links on the web are in the simple form of href="". No problem there. But with Google's erstwhile reliance on PR (Page Rank) to derive its results ...sites began masking outbound links to prevent PR "leaking" from their pages and "reducing" their pages' importance to the Google algorithm. So they found ways of linking out that visitors could follow by clicking but that the Googlebot couldn't. The main ways they did this was by cloaking the link in javascript (which Google wasn't parsing), but larger and more sophisticated sites used cgi and php scripts to redirect users to the final destination. Big sites like the Yahoo directory are good examples. If you hover over the first link here you'll find that your browser description bar doesn't suggest you'll be going to but clicking on the link will take you to that destination. Google doesn't play that game as you can see here.

One way of configuring outbound links turned out to be malignant. Some sites link to their own internal page which redirects to the final destination page. So, instead of linking to your site I could link to When a visitor clicks on the link the cgi script takes them to your site but Google would look at the link and assume it was going elsewhere to within MY site (as Google doesn't execute the cgi script to see what the real destination is). This is called hijacking and over 50,000 sites have done it to you! See here. That's an allinurl search and only pages from YOUR site should be returned.

Now this is where it starts getting interesting. A bug in Google means that when another Google bot finds your real page it attributes all the content on that page to my site and then removes your page from the index because you have duplicate content (a big no no with them) to what it sees as "rightfully" belonging to my site. To be fair it was only doing that if your page's PR was higher than mine (Past tense intentional).

Malicious webmasters soon discovered this was a neat way of nicking all traffic from competing sites which had a lower PR to theirs. And without breaking any laws or search engine guidelines. The barrier to entry is low. Almost anybody can do this and no special spamming or cloaking skills are involved. Simply link to your competitor with a redirect link. And, that's it!

Right from the start - from about a year ago - webmasters were pointing out this problem to Google but it was largely ignored. Soon tens of thousands of "black hat" (spammy) webmasters were exploiting this but Google was still not acting. Tens of thousands of "innocent" websites have "disappeared" from the Google index. What can webmasters do about it? Nothing. See post #54 here (sub required). They are just sitting ducks.

Months later Google is still not acting. The discussions in webmaster forums turned to possible reasons why Google hasn't done anything. It turns out, shockingly, that they can't. The unofficial Google representative called GoogleGuy who interacts with webmasters in various forums asked for reports of this problem in message #19 in a thread called Come on Google, fix it. That was eight months ago. He's had over 10K replies/examples emailed to him since then. Browsing through the other threads I've linked to (a lot of work there for you :-)) will give you an idea of all the possible solutions mooted and the technical reasons why Google can't implement them. So more and more webmasters are getting in on the game.

Google state in their guidelines: "Please note that there is almost nothing a competitor can do to harm your ranking or have your site removed from our index". That has now become a joke. Almost any competitor can take you out of Google altogether. And now it turns out that a competitor doesn't even need to have a higher PR than you do. The large amounts of money to be made by hijacking another site (which is completely legal BTW) means that hundreds of thousands of webmasters are getting into this. It is estimated that it will take less than a year for the Google search engine to become so inundated by this problem that it will become virtually useless.

Happy reading.

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