Links are one of the most important factors in rankings. So why not using hidden links? Links which are not seen by users, but seen but search engines.

Hidden links could be done in few ways:

- writing the text with the same color as background's
- using CSS div with hidden attribute
- seting font's size at 0
- including text behind a flash/image

Easy to do it. So why not?

Let's see what Google say about hidden links:
"If your site is perceived to contain hidden text and links that are deceptive in intent, your site may be removed from the Google index, and will not appear in search results pages. " (Hidden text and links)

This means that Google considers hidden links "illegal". So, if you want to do it, do it :) but you will support consequences if you are caught.