Skimming and Blindlinks

Skimming and blindlinks are two common techniques used by TGPs and other websites to trick surfers into going to another website. The usual motivation is that the webmaster gets some kind of credit if they direct visitors to the target website.

While these two techniques have the same effect, they operate differently. Blindlinks is more of a social engineering technique, while skimming relies on technology.

Blindlinks

A blindlink is a link to a target website that looks like a normal gallery listing. If these links are identified in some way; either the description, or with an icon or different color for example ... then we did not consider the link to be blind.

An example of blindlinking to this site would be:

• 8 Pictures of Trees
• 8 Pictures of Flower
• 8 Pictures of Beaches
• 8 Pictures of Sunsets

The third listing is blind ... the surfer is expecting to go to another picture gallery but instead ends up at the front page of this website (and buys our software?!).

There are degrees of blindness. We gave the lowest marks to TGPs that contained blindlinks, but also altered the surfer's status area using javascript to hide the true destination of the link.

Redirection Linking

A website that uses redirection linking does not link directly to its galleries. Instead, it links to a script on its server, passing some kind of token to the script in the url's query string. For example the links are of the form:

Most sites that use this technique use either the form of 1/. or 2/. for all their links. We prefer the first form because at the least, the surfer can see where they are supposed to go.

When you click on one of these link, you are (hopefully) redirected to where you want to go. The webmaster can do this in a number of ways, but the most common is to use HTTP redirection (Click here for a simple introduction to HTTP).

For example, we downloaded the MadThumbs TGP that uses redirection and "clicked" on one of its galleries. A log of the HTTP requests and server responses is displayed below.

There are 3 request-response exchanges. For most webpages there is only 1 request-response exchange between your browser and the server.

• Exchange 1: Is from our computer to www.madthumbs.com ... www.madthumbs.com responds with a 302 redirection back to another address on its server.
• Exchange 2: Following the rules of HTTP, we make another request to the "Location" of the 302 response ... www.madthumbs.com responds with another 302 redirection with the "Location:" of a gallery.
• Exchange 3: Again following HTTP rules, we make a third request to the "Location" of the last 302 response. This time the "Location" is the actual gallery, and we get the final webpage in the response.

Your browser does all of this automatically ... but it does leave room for some dirty tricks...

Skimming

Unlike blindlinks, skimming only works on sites that use redirection linking.

Unlike blindlinks, you are not "misdirected" when you click on a specific listing. Instead, you can be "misdirected" when you click on any gallery.

The exact formula as to when you are "misdirected" is up to the webmaster. Typically we have seen systems such as every 5th and 6th click is misdirected ... or the 3rd, 7th and 12th clicks are misdirected.

It is the use of harmless cookies that allow the server to track whether this is your 1st, 2nd, 3rd etc click. Cookies are an addition to the HTTP specification that give webmasters a way to communicate state (or data) across a number of HTTP request/response exchanges.

Below is another log for when we "clicked" on a .second gallery.

In the above exchanges, we are setting and sending cookies like any browser software would do.

The lines in red have changed from the first galleries logs, and this is how the server keeps track of how many clicks we have made.

If the webmaster configured their site to skim, it could easily misdirect us to some other web page "Location" when it sends either the first or second 302 redirection response.

Please note: The above logs do not show that www.madthumbs.com is skimming as in both cases the final 302 "Location:" address was the gallery we expected. However, if we continued to click on galleries we could have skimmed.

For examples of skimming that our crawler found on the 17th January 2005, please see the "Galleries" section of : Sticky Hole, Teeniefiles , Bunnyteens , Bunnyteens and, Madthumbs. Our study showed us that the great majority of TGPs that use redirection linking do skim ... some worse than others.

Conclusion

We recommend only returning to websites that do not use skimming or blindlinks. While you are there, check out some of the advertised links to say thanks to the webmaster for not resort to tricks!