Hidding "hidden" layers with JavaScript

Do you think Google will notice hidden layers if the div tag is JavaScript?

[STMLJohn]

I'm looking at a site at the moment that has been optimised by a well known UK SEO company. It contains a hidden layer, but the <div> tag has been written in using JavaScript, in the same way that you might hide a "mailto:" from an email harvester.

Obviously this is spam, but do you know if Google might notice this? Do you think this method would make much difference (there is a lot of body text in the hidden layer)?

Also, what happens if the site is penalised, but they change their SEO company? How long would a penalty last once the layer was removed?

[4eyes]

Google doesn't notice 'hidden' layers very well at all - there are a 'shed-load' of ways you can do this without incurring an automatic ban.

You can't easily hide it from your competitors though, and if they spam-report you and Google does a hand inspection you are toast.

In short, its a risk.

Will my competitors notice?
Will they spam report?
Will Google act on it?

It seems there are still plenty of people prepared to take the risk.

[STMLJohn]

I agree - it's a risk.

Knowing the SEO company involved though, I'm wondering if they regularly take this kind of risk. As someone with an interest in SEO, if it were me doing this, I'd consider myself to be taking double the risk. If the site is penalised, I've lost both my client's listings AND my reputation. And probably my clients too.