Vista Tutorial - “Help us with spammers” message

A friend has started getting a ‘Help us with spammers’ message every
time she wants to use Windows Live Messenger to send or receive Hotmail
messages. This asks her to key in a series of letters and numbers.

She is finding this doubly frustrating as often it is not clear what is
part of the data to be input and what is part of the background, with
the result that this security check fails and she has to re-input the data.

None of our other friends using Windows Live Messenger seems to be
having to take this security check. As far as I can see it is not a
virus or spyware.

Grateful for any advice on how it can be switched off.