Some minutes back I wanted to download a file from RapidShare.com. But it looks like they've changed the method they use to ensure that a user is indeed a human. The new method they use- still a CAPTCHA- is not only confusing, it's quite difficult too. One sees the following text when presented with security question:-
Please enter the following code when downloading. Only enter symbols attached to a cat. This is for security reasons. Premium users can jump this step.
And an image like this one is visible
A new user will almost certainly think that every symbol has a cat attached to it. However, since the field to enter the security code is only 4 character long (while there are 7 characters in the image above), it means that some characters out of the above do not have a cat attached to them.
Coming to the point, the key here is to enter those characters which have a head of a cat visible. In the above case, it's NNOO. Characters that don't have a head are invalid ones.
As a side note, I feel that this new system deployed by RapidShare is unnecessarily confusing. CAPTCHA systems used by Google and Microsoft, as shown below, do the job (of ensuring that a user is a human) nicely, without spoiling the user experience.