Hidden text and links is a primary reason a site maybe seen as "untrustworthy" and is likely to suffer from a low search ranking. The reason is simple, the information you give a search engine is different to that which you are giving to your "real users". Common ways to hide text include:
using the same colour text as background
putting text behind an image
placing text (using css) off the page, i.e out of view
using a font-size zero (0)
using image alt-text incorrectly
Further to the above being used to hide links you can also:
make the link image 1px wide and tall
make the link a single character
If your site is perceived as being deceptive and untrustworthy you maybe removed from a search engines index for any period of time. If you have a developer whom is external to your business you may want to take a look to see if they have falsely helped rankings (in a black hat manner such as this) by viewing your site using a text-only browser such as LYNX.
Finally, if you find your site has been removed from indexes due to the above and you've fixed the problem contact the search engines in question and tell them you are sorry and ask for reinclusion into the engine. If you are having problems removing the text and links contact me at hello[at]andykinsey[dot]com or purchase our DIY Service (Removing Black Hat SEO).