Search Engine cloaking is when you display one version of a webpage to the search engine spiders and another to the actual visitors.

The reason sites do this can be numerous, unfortunately many do it for nefarious purposes, and the search engines don’t like it.

On this topic, Google is pretty clear: “Cloaking refers to the practice of presenting different content or URLs to users and search engines. Serving up different results based on user agent may cause your site to be perceived as deceptive and removed from the Google index.”

That said, top sites like the NYTimes.com and many similar news sites do use forms of cloaking. They often allow search engines to index content but prevent human users from seeing stories unless they register. In this case it’s okay.

Penalties, however, may hit those sites that clearly are trying to manipulate search rankings by showing search spiders one thing and humans another. That’s a no-no.

But again, there are instances where cloaking is desirable. In addition to the aforementioned news sites, some of those include sites that cater to different geographical regions, or those that are heavy into flash or non-spiderable content, or even if you are trying to hide duplicate content.

Just remember, if you go down the road of cloaking make sure you are doing it for the right reasons.