More on hiding

Other conent/link hiding techniques

Here I'll present some quick examples of hiding techniques that didn't fit into previous chapters.

1x1 pixel images/transparent images

This technique is pretty simple: a webmaster adds a very small image to a web page and uses image's alt text instead of a usual anchor text. Since the image is very small or transparent it is almost impossible to spot such link for humans. This method was very popular some time ago, but at the moment search engine robots get smarter. Since it's really easy to find image size a very small (1x1 pixel) image rises suspicion flag.

Frames/iframes

This technique is more effective when used in combination with some nice CSS rules to make a frame appear as a consistent part of the web page. robots.txt rules can also be used to tell robots not to index page in iframe.

Noscript tag

This tag is designed to hold alternative content which is shown to a user who has JavaScript turned off. Since almost every user has JavaScript on the contents of noscript tag remains invisible to them.

Cloaking

Cloaking is almost always considered a black hat seo technique. Cloaking is a method where different content versions are presented to human visitors and search engine robots.

Usually it works in this way: server side script tries to find out if a user requesting the page is robot or human either by checking user's IP address or HTTP header User-agent string (or both). User agents in HTTP headers are identified in a similar way as in robots.txt rules.

A tip: I've seen somewhere the following php code that was suggested as a reliable robot detection algorithm:

$is_robot = (strpos($_SERVER['HTTP_USER_AGENT'], '+http') === false);

It is based on presumption that all search engine robots leave their home url in their User-agent setting. This is absolutely false. Many robots do not specify their home urls. To learn more about User-agent identifiers you can simply look at your server logs; also do not forget to check robots.txt chapter if you skipped it.

More advanced client detection techniques can also be based on the client's behavior analysis after a few page requests.

Flash/Java applets

Flash was considered terra incognita for search engine spiders for quite a long time. But recently Google announced that they already index some parts of Flash (and I believe, that their skills of Flash reading will improve in the future). So this technique can not be considered as a very reliable one.

A similar alternative technique is Java applets. Search engines are not indexing applets content yet. And I can not be sure about the future. However, it is very easy to extract some information from Java, so Java applets should be used with care.

Robots-nocontent class

In May 2007 Yahoo introduced robots-nocontent html attribute which was meant to hide any part of a page from Yahoo robot. This attribute can be used on any html element, like:

<div class="robots-nocontent">

Yahoo robot (slurp) should read this as: content in the div marked with this attribute is unimportant. The biggest downside of this technique is that it works only in Yahoo. So it is not very popular among seo web masters.

Final words

I tried to sketch the most popular techniques of content/links hiding. However, a lot of other methods can be met online and you can also invent your own ways. The techniques I described above are more powerful when used together (e.g., JavaScript + CSS + robots.txt).

In any case, I do not advocate content/link hiding when it is used to manipulate search engine rankings in an unethical way. Still, if you do this in a good deed, I hope this article will give you a clue on how to hide your secrets properly in order not to get penalized accidentally. Also this should help you spot unethical guys and not mess with them.

Recommendations for further reading:

This article is a part of SEO design patterns - hiding links. You could also be interested in other articles from this series: